I didn't think of that when I watched it (although I was a little distracted when I watched it, might have to see it again) but now you mention it, it could very well be BPD. She did show a lot of the traits, and yes i agree, she played it very well and her character was totally lovable and even beautiful. Not sure if she was meant to be BPD as such, but either way the film was really enjoyable and one of the best movies about mental illness ive seen in a while. They don't make enough of them and to this quality or without being hollywood-i-fied as you said. (So true)
I've always wanted to write a script for a film about someone with BPD and other mental illnessess. This film gave me the passion to want to write it.