A meeting with the school counsellor is a great idea. You don't want to have to deal with this,alone. Besides, they have probably seen this before and might have resources and pointers you could use.

Talking to the school councillor is a good idea. It might also be worth sending your sd's therapist a message letting them know what is going on and asking for advice as how to help your sd feel comfortable going to school.

My YSD pushed to do her final year of HS remote.. she claimed she only needed 2 classes and would graduate early.  She was a good student, her grandparents said she could live with them and do it. (mom would allow her to move to the rural grandparents home.. and her dad was working offshore so it was the only real option.)  I had to be her online reviewer.  Well.. turns out it was more like 4 classes.. we had to pay out of pocket and it was pulling teeth to get stuff done and she spent the majority of her time on snapchat as far as we can tell.   It also really didn't happen "early".. but ultimately she did graduate.

Unless you have a highly motivated kid, remote doesn't work well and even when they are.. it can still be a struggle to get them to keep up with the work.

I am guessing there were more interpersonal things going on.. that it's more the social aspect that she wants to avoid.

The on-line school thing is tough. It takes a certain type of person to do it and I'm not sure your SD is that kind of person. If she had drive, maybe but she has no drive. If she'd been home schooled or on-line schooled for years, maybe but she had\sn't. If her parents/Stepparents were all on the same page, maybe but her parents aren't even in the same library let alone the same page or book. 

I'd give the school a call. What's there to lose?

 SD staying home doing "virtual school" for grades 10, 11, 12 while you work from home? Hard nope! You're going to have to have a plan in place to ensure this doesn't happen.

Just a couple things... What happened with DHs emergency order to switch custody to crazy?

Is there still an option to send SD to a facility for troubled teens/mental health program after she tried to get your husband arrested by calling the police and everything else? And now she refuses to go to school?

My SS who is almost 19 now.. I believe he did virtual school for a while also while he lived at his moms house... Same reason... All the schools suck and he doesn't get along with anyone... In the end he finished high school at a college and obtained a GED for high school equivalency... 

Anyhow your SD is certainly testing the boundaries and limits here... Whatever route you end up going if it was myself I would tell my husband I didn't care what happens but my hard boundary is that SD is not allowed to be doing virtual school at our house while I was working from home so he needs to find a solution.. 

I might be tempted to say "Damn right I don't want to watch you all day, look how you act!" Wasn't she the one who was supposed to be in an intensive outpatient mental health program? Whoever decided she didn't need it couldn't have been more wrong. She won't graduate if she has to be responsible for herself for 3 years. Stand your ground on this one. If she stops going to school, do not allow her to sit in your house all day. 

When dealing with people who are manipulative, I have found it's best to name what they are doing.

So, when SD says, "It's just because you don't want me here."

I would say, "That's really manipulative. You're trying to make us feel guilty for not giving you your way. You know we want you here. What we don't want it is the constant battles from trying to hold you accountable for homeschooling."

Call it out every single time.

As having you have her at your house as she does online schooling.  She with BM. I Would disengage from all of this nonsense .  SD is running the show, you have no say in any of this .except not be part of it.  SD isn't going to do well no matter where she goes .  The school will want to get her out.    
Bigger question is what happens after school.?  If she can't deal with school,  She can't deal with work. ?  Where is she going to stay ? What is she going to do :

Teens are innately social. The fact that she has no friends at all and wants to completely isolate herself is alarming. I'd definitely start with talking to the school counselor to find out how to proceed if she actually refuses to go to school - I can't imagine that they'd recommend physically forcing her to attend, though I have no idea what the alternative would be.

But after that, her medication situation may need to be addressed. If she's taking antidepressants or a mood stabilizer, an adjustment may be in order because her mood and behavior sounds like it continues to be pretty erratic. 

Sd18 Princess Powersulk did that and was on the brink of failing because not doing the work. Honestly you have to really try to fail the online school. The very fact that these kids think they can force the adults into putting up with their BS is beyond me, but Im seeing it play out before me.

Great God Almighty!

I cannot believe what I’m reading. So, things have come to the point where children are so outrageously pandered to that they can refuse to attend school and folks actually look for alternatives, rather than suggest that parents behave like parents and fall down laughing at the demands of a manipulative brat. I would love to have ruled the roost when I was a kid but, thankfully, the very notion was unthinkable.

TrueNorth (you poor girl!), your SD behaves like a toddler whose parents have always given in to her tantrums rather than exercise some reasonable boundaries. Your DH’s virtual toddler (who refuses to blow her nose; more ‘pity me’ manoeuvring) has enjoyed total power for so long that no ridiculous demand is beyond her grasp.

 So, the little brat accuses you of not wanting her around? I’d answer with, “Damn straight! I refuse to be responsible for an unstable teenager who makes unfounded accusations!” FFSake, stop pussyfooting around this master manipulator! Who are the adults here?

The first thing your SO needs to do is talk to her school about what happens if a child refuses to go to school.  What are his rights and obligations as a parent.  He should relay that remote school is not an option for his daughter.. and that she is (I think) in counseling, but that this recent refusal is new and he does not know what will happen if she does in fact refuse to go through the doors.

She is a teen.. he can't wrestle her into the car.. he can't sit in class and force her to stay.  

Has he looked into any kind of boarding school options for her?  maybe she would benefit from those.. though I know they come at a cost.

I kinda understand from the kid perspective if school is a crappy environment and nothing can be done to change it except leave / go to another school or home school

Problem is some of these skids / kids behavior is so atrocious that they're unbearable to be around for extended periods of time especially without high levels of structure and when you're working from home you cannot provide that structure as well as someone who doesn't have the responsibility of an employer 

I would have been highly triggered if my ex partner / former skids expected me to take care of them/home school them AND work a 9-5 

These Disney parents better be compensating for this overtime work they're expecting helping to raise their spawns

otherwise go homeschool and lock in with the breeder .... 

NO and no!!!!

Could you imagine this kid doing online school at home.. Making lunch messes... Probably laying around doing nothing most of the day... Ugggh. I feel for you TrueNorth

When virtual school was a thing for the kids during covid most of these kids did one hour at most of school per day. My step kids did nothing. 

The other thing to consider is that college and universities may penalize you in some way for doing virtual school versus in class. Some colleges may not take the virtual class credits at the same value as the in person courses (assuming if SD wanted to go to college after high school)? 

About SD.  The school is offering on line schooling.  Covering there a$$ by law.  Schools don't want to deal with students who really don't want to be there and the kids parents have no control over that kid.  This kid needs to be put on drugs and major mental health help.  
'Get this kid out of your home if BM doesn't care then it's BM problem

Your SD is still young at age 15. As she gets to be an older teen the consequences of all of her  "refusals" are only going to get worse for her and I don't think she realizes this at this point. Sure, she might be able to get away with stuff now. And hopefully some of this gets shut down.

However no one in the real world is going to tolerate this as she becomes older and she may find herself in some tough places when she can't just magically coast on by without a plan, a job, education, house.... Just exactly what does she plan on doing with her life. She will only get so far. I don't think she'll be living at daddy's house forever with no job and schooling. 

This kid needs to be in the system. Have a judge climb her ass, tell her to get her ass to class and apply the looming consequence of her attending a disciplinary school for adjudicated teens.

You do not have much time. She can drop out at 16 which is less than a year.  I would also make it clear to DH that if she does drop out, she will no longer be in your home.  Hand him the print outs for forcing emancipation on a minor.  She wants to play adult, she can support, house, and feed herself.

I had my similar moment when I was 16.  I had bombed my sophomore year of HS. My parents enrolled me in military school for my second sophomore year.  Mom, dad, and I were waiting for him to board his flight to fly back home. Mom and I had another several weeks before my report date to school.  I informed my parents I would not go to military school.  Dad quietly picked up his brief case, opened it, wrote me a check for $500 and told me I was 16 and it was my choice but that check was the last family resources I would get and to make sure to contact them when I found a place to live.

I held that check for a very few seconds that felt like hours. Handed the check back, and said that I would go.

That is a memory that I very likely supress. It only arrises when something triggers it.

Yes, get this kid some therap. However, in my own experience it is time for parental hardball. There is no time for anything that is not immediately and assertive. She gets her ass in class, she keeps her mouth shut, she gets the common denominator speech day and and day out with zero tolerance for the "school suckes, the teachers are stupid, the other kids are idiots" bullshit. She and she alone is the common denominator and she  needs a parental boot up her ass.  School, or at 16 she gets to experience how to suppor herself completely.

My experience was eye opening and set the foundation for eventually performing as a viable adult.  If my parents had tolerated me continuing down the path I was on, I would not have the life I have. That what if, would not have turned out well for me.

Parents need clarity that their job is to create viable adults. Each kid is different, however, the goal is the same regardless of the kid.  When the kid won't get out of their own way, the parent needs to make sure that kid keeps their head out of their own ass.

We had a near miss with SS. That was at Military School.  The Spermidiot hacked the school firewall and he and SS would stay up all night playing WoW to the point that SS was a comatose zombie in class failing the only class in the Fall of Sr. year that he had to pass to graduate in the spring.  That class was not offered in the Spring or summer so we would have had to pay another full year of tuition for him to finish and we had zero trust in SS that he would actually do the work to graduated.  He had kicked ass his Jr year. Top of his class, top performance in the Corps of Cadets, top leader, top athelete (qualified for the national championships in military drill), top musician in the Corps military marching band.   But, instead of spending that money, we withdrew him at Christmas break, brought him home, enrolled him our local HS, He had one semester to graduate.  To make our point very clear, we made a visit to the local homeless camp to highlight where he would be dropped off on what should be his graduation day if his Spermidiot did not send him a bus ticket.

That kid was terrified for the next 5mos and worked his ass off. He did graduate on time.  It was not a fun time for any of us, but it was what we thought necessary to get him a diploma and learn that he and he alone was responsible for his moving forward in life.

Good luck with this one.