No, you are not wrong.  Except in your choice of an SO.

Your bio children are right. She is not a nice person.

Why is everyone at her beck and call, changing/ruining plans etc? Put your foot down!

I remember every year when me and hubby and our 2 kids flew back to Australia for winter holidays to spend time with my elderly husband and just family time, my husband always had to give sd's a heads up and then they would always have an emergency and hubby was expected to prove they came first.

one time we were halfway into our trip and eldest sd was 24.5 messages daddy demanding he pull strings to get her 1st cousin from batshit crazy biomums side a job at hubby's company.

firstly- she bombed the interview so bad she didn't even meet basic criteria, secondly- she looked 10 yrs old, thirdly- she had had no relationship with hubby since he was married to batshit crazy exwife and even more so after the divorce. Why would my husband do a favour for someone he doesn't Know.

hubby told his daughter he was o/seas and couldn't do anything and if sd's cousin sucked big time at interview which is obvious since she didn't meet basic criteria for a shortlist interview, it was out if hubbys control. Sd sulked for a few months.

anytime we had family events and hubby wanted to pick sd's up, they changed pickup times last min or pickup locations and we were expected to cater to them despite us having a 1 & 2.5 yr old kids. I gave up with these last min cancellations and told hubby no more.

its all a manipulative game for hubby to prove his love and that we weren't important. I refused to play that game and disengaged and refused to go to any events hubby's feral daughters will be at

ss was 22.5 and as we were leaving home to take our kids for their immunisation at the private hospital they were born at, ss demanded hubby taking him shopping for supplies for college. He is perfectly capable of taking his motorbike but demanded hubby essentially ditch us for his non urgent crap.
 

Another time we had booked a mini getaway, ss as usual comes home unannounced and hubby tells him tomorrow we are going for a mini getaway and he needs to book an uber to go back to university. I kid you not, ss demanded my husband drive back home from our hotel which is 1hr drive away if no traffic and often takes 1.5hrs to drive, then as usual hubby would have to wait 30 mins for ss as he is never on time. Then a 2 hr drive to his uni and with bad traffic tag on another 30-40mins then its 30mins-60 mins drive to our hotel if lucky. Ss expected hubby ditch me and our 2 kids aged 1 & 2.5 for 4.5-5 hours at least to play chauffeur during our romantic holiday. 
 

my husband is not an idiot and knew during a se y Romantic getaway, that ditching me is a big no no. So hubby gave him 2 options, tomorrow he comes with us to the hotel to have lunch and book an uber back to uni or he stays home and books an uber the following day (sunday) back to uni. Ss told his dad "no pick me up from home on sunday", hubby said that isn't happening, ss was forced to go the next day and book an uber

fridays hubby always has board meetings, ss would message hubby at 3.30pm demanding hubby pick him up now from college which is a 1.5 hr drive away despite knowing well in advance he was ready for pickup friday. Its just part of the manipulative crap of having daddy prove they're more important 

Your SO needs better boundaries with her. Where is caninelover? This girl sounds like her SD, Bratty McBratface.  Caninelover pushed her SO to set boundaries and not allow the skid to run the show. 

if your husband isn't getting it, start keeping a chart or notes w/ date/time spent w/ daughter that involved her and excluded everyone else.

She is a bratzilla. Your SO is the problem if he does not see the problem. He needs to make sure you are comfortable and don't freeze your ass off in the back seat for example. Also, I was raised to always allow parents to sit in front. (Unless car sick or some good reason.) It will be an uphill battle if your SO is clueless how life works. Try step couple counseling 

She's 22. I'd say, get daddy cut the apron strings. He won't be doing her any favours. 

Thanksgiving of this year-she calls her dad at 10am that day and wants to visit re: her classes etc for college. She is supposed to graduate in December with a BS in exercise science but now wants to go back to school to be an Orthodentist (sp).    He had to leave the house and spend 3 hrs at a coffee shop. 

If SD was in her last semester and wants to talk about 'classes' my bet is that what was discussed is how much of dental school SO will be paying for. 
Guard your finances. SO should be paying his fair share of joint bills, and funding his retirement, before he contributes to SD's graduate school. 

And no, SO did not have to leave. He could have done it another time. Have to leave on a holiday is reserved for SD has been in an accident and he needs to go to the hospital.

You have a SO problem. SD speaks and he jumps.

Your SO needs to nip it in the bud or it will only get worse.  I've dealt with three SD for over 36 years and to this day they demand to have both parents every year with them for their birthdays, their children's birthdays, Easter, Thanksgiving and Christmas.  After all these years I finally said enough is enough and now it's a real nightmare.  YSD showed up on Christmas with her choice of food, with her husband, son (18 years old) and sat down at our table and eat with her dad, son and my SO.  Stayed for 8 hours....She didn't let me or SO know she was coming with a full course meal.  So, much for enjoying a BBQ with my SO.

MSD (middle step daughter) texted on Christmas and said she was with BM on Christmas and would be at our place the next day.

OSD lives 3 hours away and begged for us to drive there for Christmas Eve.  I couldn't believe my SO didn't go.

YSD birthday is on 8 Jan 2022...can't wait to see if SO goes, because this year it will be without me!

I would suggest, cutting the strings now, unless you wan't to play power struggle with your SD.

Your kids are right, she's not very nice, or considerate for that matter.

As much as we want to blame it on the brats, your man is your biggest issue because he's so Pu**y Whipped by his own daughter. She says, "jump", and daddy says, "How high hoooney?" He's been doing tricks for her like her own personal dog all her life, and this dynamic has worked for THEM, but it's not working for you.

What man makes his wife sit in the back seat while SD freezes her out? At least he did say something, LATER, but metaphorically, SD put you exactly where SHE wants you, in the back seaty and freezing, while daddy remains her ever silent lap dog. When he did nothing and allowed you to be placed in the back seat, that was affirmation to his brat as to exactly where you stand in her mind.

You need to take up Boundaries 101 with your DH, and get him on board. Daddy needs to retrieve his balls from his daughter's Prada purse. This sounds miserable. You two can never have any time together, as she deliberately sabotages it.

Wishing you better in 2022~

When it is their SO where the overwhelming majority of the blame really belongs.

Ball-less former failed family breeder, failed parents are where the blame lies.  As much and as easy as it to blame the kids.  Who far more often as not are far from blameless.

IMHO of course.