undines
Local authority? They will do nothing, because she is NOT technically homeless - she's sitting pretty with Mum and Dad! Also, there have been some rather glib comments about renting, getting her own place etc. but that is horrendously expensive, now. Haven't you heard there is a housing crisis? Really sympathise with both sides, and agree with those who suggest talking about it and trying to find a solution, or at least some way to alleviate things. Good luck!
If Mum and Dad are not prepared to offer a home, she is homeless. I was in her position once, as was my SIL and that is what we were told. As for renting, we do not know her situation regarding money but she might well be able to claim benefits. The LHA will give advice.
When I left my mother's house, we had 5 kids in a one bed flat...having our own space albeit very cramped was much better than trying to live with parents!