Not to alarm you op, but you have tk be prepared for that 'whatever that entails' part.
Honestly, the situation is very similar to my nephew:
Adopted by dsis at 7, diagnosed with asd PDA profile, Adhd around similar age, trauma in early childhood too).
At 18 the wheels fell off, dsis lost any control she may have had (and actually, her approach was pretty authoritarian, tried to gain control by banning his phone, stopping his allowance etc). She tried literally every avenue open to her (including power of attorney, sectioning), nephew just couldn't engage,not.with authorities, not with her, not with anyone. In the end, I'm afraid she ended up putting herself and remaining family first and told him he could no longer live with them.
He's currently jobless, homeless, penniless, and becoming increasingly involved incrime. While PDAers (if that is what we're dealing with) often can and do find their niche, the reality is that the most extreme cases can and do spiral - precisely because the young person cannot engage with the people they need to.
It upsets me to say that because I've always been a 'no problem is insurmountable' type of person, and I'll work tirelessly to find a solution. But if the new approach doesn't work, the old approach hasn't either, then you may need to be prepared to watch her fall. An impossible ask of any parent, yet sometimes necessary to preserve the remaining family.