By BPD do you mean Borderline Personality Disorder? Some people mistake BPD to mean BiPolar Disorder.
Whichever she has, of those two disorders, are very serious, and she should be treated by a professional.
I will guess that it is Borderline Personality Disorder by her behavior. She more than likely doesn't realize that she is saying a lot of things to you that hurt you, expecting so much of you, threatening to get a restraining order on you, and saying that she doesn't want you to be her friend anymore. There are many other aspects to BPD...and one very bad one is self-harming, which she may start to do. The self-harming, is usually cutting one's self to feel physical pain to not have to face the emotional pain she is going through. Some people call self-harmers "cutters." I don't know if you read about that when you researched BPD.
Is there anyone that is in her family or close to her that may listen to you and realize she needs help?
If she sees a psychiatrist and gets help through psychotherapy and/or (more than likely) medication, she will most likely be able to get a grip on reality, and, in turn, be your friend again.
The reason I know all this is because I was diagnosed with BPD years back. I was a cutter. I am now taking medication for that and for other psychiatric problems, and I am doing quite well.
If you wish to talk more about it, you may PM me. I will go into more detail with you about my experience with BPD.
If not, the best to you in somehow getting her to seek help!