Hold up... Why don't you get a say on an adult moving in?? That is a no go. If SD wants to drop out of school she better have a plan and be prepared to adult. This would be a line in the sand thing for me. 

Have an honest conversation with him and tell him how you feel. No ultimatums. A request that his daughter not move in because it will take a huge toll on your marriage. If he ignores you and moves her in anyway, then maybe it’s time to cut ties.

 I don't get any say so on her moving in. 

YES YOU DO! They're going to discuss their daughter's future? Well YOU are going to be there to discuss your HOME! You pay the bills and that alone gives you the right to your say. What happens in your home is your responsibility and you are damn well going to be part of that decision. If  you're not invited, go anyway. Let them know that they'll have to reckon with you and that they need to find another solution because your home is not going to be it.

Now go in there fighting!

1.  Some schools will give a partial refund, see if she can get.

2. DH must tell her IF she moves back in, she pays rent every week.  If it won't leave her much spending money, tough nuggies.   And she must be civil to you, clean up after self, etc.   This may discouraging her from coming home. 

You know that is SD moves in it’s going to be fighting all the time.  Tell DH. NO, she not moving in!! Not into your house.  Let BF and BM figure out what to do with her !!  But not into your house.  Make a stand, once she in your house she will never leave 

She's mama's 12 year-old princess with her smartphone, big data plan, newest computer in the house, three gaming consoles jammed full of games, and anything else she's ever wanted. I'm the only one who has a job and earns money (bio-dad was a short-term boyfriend; he's completely out of the picture and pays zero support). She's a by-the-book screen addict, enttiled to 24x7 entertainment. No boredom for princess.

She doesn't know the phrases please or thank you, to me or anybody else, and has no chores. She does have a kindle library full of high quality books and hasn't read a single page of any of them -- literally, nothing -- though her mom insists education is important and wants her in an expensive English language program. Princess sets the rules: if she wants to go somewhere I'm supposed to snap to attention (mama doesn't like to drive). If she doesn't want to leave I'm to wait around, like a good chaffeur. She insults me, puts me down, yells at me.

She has a filthy mouth: every other word is the f-word or something similar. Her mom is her biggest fan and insists it's just me. It's a concidence that her former best friend's mom banned her from being around, that she hates every other girl at school except one, and that all her "friends" besides one are online. Unsurprinsgly her grades stink; she's not flunking out but they're completely mediocre.

I call it the 2/20 syndrome. She has the responsibilities and expectations of a two year old toddler yet the rights of a 20 year-old, though I've never met such an ill-mannered 20 year-old.

Getting back to the point if the marriage lasts until she leaves there's no way she's coming back. I left home at 17. Her mom left home at 16 (neither of were runaways - we finished school early). She's on track to finish at 17 and when she's off to college, or cooking school, or anywhere else I'm done. I hope she finds a boyfriend in a few years and mooches off his family instead of me.

I really like this forum. For now on I'm just going to ignore her. No more favors, no more listening to the demands, no more buying her anything. I'm on the fence about cancelling the phone plan because her mama tends to freak out (that's the main way princess holds power and she knows it: it's easy to prod mama into an epic episode of verbal and physical abuse). 

I posted this on your prior blog post:

Oh heck no way!  You have to sit down and have a very calm, very cold (remain icy cold!), talk with your DH.  Have your talking points laid out on paper so he can follow them.  Allow some wiggle room for negotiation with him, but DO NOT ALLOW this - if she does move in here are the stipulations about rent, how much, when it's due.  You can also find actual rental agreement templates on line.  Print one or two out and tell DH she WILL be signing a rental agreement (it's called being an adult and responsible, esp. if she decides no college...payment due dates, quiet hours, cleanliness requirements) like this one or that one.  DH and BM do not get to unilaterally decide what will affect your living situation.

Adults live under rules - she's made an adult choice and she lives with the consequences or YOU go.

Because you keep posting the SAME stuff over and over and over, whining......yes WHINING how DH doesn't support you, all your money goes to his skids, etc etc etc......you know what else hasn't changed?  YOU.  YOU are putting up with this.  You have been posting here for over a year and very little, if anything, has changed.  Is your DH a disney-dad-guilt-parent?  Yes.  Of course he is.  You cannot change him.  You can only change yourself and how you act/react to things.  I'll be damned if I would let my partner walk all over me and treat me as crappy as yours is.  Everyone drops the "counseling" line and I'm going to as well.......maybe counseling for yourself can help you get some perspective in why you allow yourself to be treated this way.

If SD moves in, it's because you ALLOWED it.  "I don't get any say so in her moving in......."   That is BS and a copout.  I would really love to read a post of yours where you finally speak up for yourself, put your foot down, say NO and stick to it.  DH is not going to change.  SD is not going to change.  Unless you are willing to speak UP and stick to your guns, NOTHING will change.  This may sound harsh, but I'm trying to shake some sense into you.

I've been in a similar situation and it royally sucked.  When DH and I first married I didn't think I had any choice about his then 29 yr old jobless stoner son moving in so I just dealt with it.  He moved in and out over several months and I finally put my foot down since I saw no end in sight.  It almost ended out marriage but there was no way I could keep living with an almost 30 yr old man who wanted his teenage lifestyle back.  If I could go back in time I would have said NO at the beginning and had the hill to die on battle then.  

If you feel truly have no choice about SD moving in and it's going to happen anyway you still have choices.  SD wants to live w/daddee so she doesn't have to adult, she wants to be taken care of.  You're going to have to practice being the WORST hostess ever. 

Do not clean whatever room she is moving into or lift a finger to help get anything ready for her. You're busy right? Work some overtime or go to the gym, whatever you do be completely unavailble to help daddee get her room ready.  

Don't cook or shop for her. She's a grown woman and can meet those needs herself. If she needs someone to get something for her, refer her to her father because....you're a responsible woman who has a job and you don't have time to take care of another grown capable woman. 

Got a dog or cat? Can you put a dried turd in the corner of her closet?  Maybe a few springs needs to come loose in her mattress.  

Bottom line is that the girl needs to be made so uncomfortable that she wants to leave!