It's very possible she has BPD. I'm speaking from the experience of someone who has it and has also engaged in (and is in therapy for engaging in) these behaviors in relationships.

I have a tendency to dive in too quickly, and am dealing with the aftermath of that right now (though it was with someone I'd known for pretty much ever). Anyway, whatever, I don't want to come off as trying to justify the behavior; it's not really excusable. But it comes from a pretty wounded place.

I tend to shy away from relationships because I know how I am, and I know how they usually end. In the rare occasion I do end up dating, I somehow find that guy who is as broken as I am, and it tends to be pretty volatile and destructive for both of us. I'm, fortunately, learning to recognize when things aren't working even when I want them to and starting to be able to back out of things instead of completely sabotage them. Starting to.

Anyway. This isn't about me. Sorry this happened to you.