Honestly OP, the more you posts the more frustrated I get with you 😵💫😂😂
Forget what works for others, forget what the FB groups advise .. what works for one won’t work for another. Stop asking us “what will I say when dd says xyz”, “how should I react now” etc. You’re a grown woman with grown, adult children. Don’t listen to her crap about it all being your fault - it’s not! I’d also stop the uni talk for now, it’s going nowhere, I don’t even believe it’s what your dd wants - it’s just another way to blame you and wind you up.
Write yourself a list of what you want dd to do going forward, daily and weekly, your expectations of her - ie make her bed every day, shower and dress every day, help with meal prep once per week (set day), clean her room once per week etc.
You are not asking the world of her, you’re giving her basic daily living expectations for now. Then move on to other things once this is sorted and achieved.
Find your confidence m because honestly, she’s playing you like a fiddle. You’re tying yourself up in knots, analysing everything you do and say, when actually, you’ve done nothing wrong.
Forget the PDA stuff. She doesn’t have a diagnosis, she wouldn’t engage to get a diagnosis, her problems are stemming from inside herself to begin with. That may not be the issue here. Just deal with what you know and have got right now. I genuinely think you’re confusing yourself and making yourself worse the more you’re trying to think, work out and solve.