Aw jeez, Offred, have you eaten something that doesn't agree with you?
Having read carer's thread in Chat, if this young girl was being treated in such a blatantly oppressive way by a dp or dh, you'd be the first to say 'leave the bastard'.
So, her df is colluding with his ex in punishing their dd in a manner that owes more to the Victorian age than the 21st century, carer? Shame on them.
Unsurprisingly, I'm with Birds. Your dn has been able to vote with her feet for some considerable time now and, if she is minded to do so, she can let her tootsies do the walking to her local authority's SS offices while they are still obliged to accomodate her. If she leaves it until she's 18 her current statutory entitlement will decrease to approximately zero.
If I were you I'd arrange to meet up with her, listen to what she's got to say and, if appropriate, appraise her of her rights, slip her a mobile phone, and assure her that I was available 24/7 should she decide she's had enough of her dps. But that's me - the scent of injustice has always been my downfall bete noir and I very much doubt that's going to change any time soon.
Alternatively, you can buy her dps individual copies of 'How to talk so that kids will listen and listen so that kids will talk' but I'm guessing a) it's far too late for them to learn and b) they're so far up themselves they'll have no interest in doing so.