She needs a proper assessment. If she won't go for help there's nothing you can do except encourage her to do so. Eventually she will probably seek help if she's not happy and struggling.
She will probably struggle at uni so prepare for phone calls, maybe dropping out and back in etc. But at least you'll get a bit of breathing space. She may get the help she needs at uni- student support services, counselling etc.
if she is violent again she will have to leave the house) but I think tough love has never worked with her before so it won't work now.
If she's made to leave the house if she's violent again, I think that's a reasonable red line to have, especially if it's effecting your other children. You can support her without letting her stomp on you all, be violent and nasty etc.
If she's nasty/violent at some point, I suppose you could say 'you need to seek help or move out.'
I'm also really hesitant to suggest she has EUPD because I think she will twist that and turn what we say against us.
Yes, I wouldn't say it unless you have a good relationship with her (it doesn't sound like your relationship is quite in the right place at the moment for you to say it.) Professionals will say it if it needs to be said, or you can suggest it to them privately without her if you're ever in a position to do so.
It's all in how people say it. I had a bitch (pardon my french) consultant try and say I had it. She was very nasty in how she put it. I virtually had PTSD as a result of how she talked to me. I had to change consulting teams. The new team have been fine. I was already thinking that I was acting a bit like someone with BPD- if she'd expressed it in a non judgmental and reasonable way rather than nastily, I would've accepted it.
I wouldn't accept it as (which my current consultant agrees- the bitch consultant was a locum I only saw twice anyway) I only have traits of it rather than the whole thing. After about 6 months I got my head round it and sought additional therapy, treatment etc. I was diagnosed with ADHD, which can have the same effect of difficulties in regulating mood etc. People can have ADHD and still be academic. I did well at uni but kept dropping in and out. I also have always had difficulties with sleep, and motivation. ADHD doesn't always make the person seem hyperactive.
I got DBT (which didn't work for me) and EMDR therapy (which I love.)
BPD traits are due to trauma, a lot of people diagnosed with it actually have PTSD. The trauma can be all sorts of things.
And then I worry that she will crash and burn at university and hurt herself or worse. Or that she will have to come home and I'm not sure I can cope any more with her living in the house permanently (I can just about cope with holidays, I think.)
Sometimes young people etc have to 'sink' a little before they can swim, in order to get the help they need from services, medication etc. If she struggles she will come to the attention of services that will help her, or seek help herself.
What is the best way to stop her being so horrible to us whilst loving her and looking after her?
I would say to her it's not ok to treat any of you like this. There's nothing wrong in you saying that. If she says she's struggling, depressed etc, or self harms, all of these are the times where you can say 'Your GP can help you.' 'All I can do is support you but I'm not a professional, you need to see your GP' etc.
Hope this helps. xxx