My over-riding point that seems to be being deliberately overlooked is bafflement at how the OP has lived 10 years with a child she seemingly doesn't care a jot about, and seems to consider a stress rather than a member of the family.
That is an appalling comment to make and a totally unfair assumption.
It seems to me that OP has cared for this child for 10 years. She has made a home for her, looked after her and attempted to parent her.
However the child's rsehole father has taken the line of least resistance when it comes to parenting. DSD wants to leave school? Let her! It's so much easier than taking an interest in her education and taking the anger and the flak the child will trow at him if he attempts to discipline her - and he doesn't want disruption, so OP* isn't allowed to try to help or guide her either.
Father doesn't try to make her go to school, get a job, stop smoking - it's all too much like hard work. But HE'S the one in charge, so what he says, goes, and OP is stuck with it.
And because the father has treated OP like a servant and undermined her authority, then the DSD treats OP the same way.
I agree that this is a desperately unhappy young woman who can't cope and is trying to harden herself against hurt by pushing everyone away - but OP can't cope with this; OP's children shouldn't have to cope with it - this girl needs professional help.
OP contact Children's Services as advised. And whatever your ex decides he wants to do, don't be part of it. If he goes, he takes his DD or arranges for her to be cared for - perhaps fostered. Even if you had no other children to think about, and wanted to do the best for her, she needs more than you can provide.
If he changes his mind about going - make him. You and your children deserve better than this,