
I have it too and I was that girlfriend in the begging of my current relationship. I recognize I was horrible towards my partner, but it wasn’t anything personal obviously. I ended up voluntarily going to the psych ward and it pretty much fixed me. The best you can do is encourage her to get professional help, and try to understand why she thinks the way she does in the meantime
Makes sense she can be super sweet and "normal" but sometimes it's like I can never do a single thing right and I'm the worst person ever which is what BPD can do to her, I try to view it as it's not her it's her BPD but getting blamed and yelled at for things that I feel are so small and minimal is taxing
Hopefully it will improve. By the time my aunt passed (cancer) she was very stable—I was about 15 at that point and I didn’t even know she had a personality disorder until after she died, I remembered her being odd and disappearing sometimes when I was young but I thought that was just… her. Like I said, by the time I was in highschool, she was pretty stable. Still had rough patches but was doing really well.
I have BPD too, intensive therapy and being able to recognize my shifts helped me, along with use of strategies or removing myself. I hope she is finding tools to ground herself and is recognizing behaviors when you bring them to her attention. It’s a difficult disorder and the amount of patience it takes can feel impossible.
I know it sounds cruel but you can’t be liable for her decisions. Worst case, have family members or friends of her’s to contact if things seem to be getting out of hand. That’s how people with BPD keep others around, by threatening the worst. Usually they’re empty threats but it’s good to let others in their circle know what’s up so they can keep an eye out