Rdgrad, you asked " how can I support her?" I think its okay for you to be sympathetic, and gently honest with her as well, if that's something you're comfortable with. Ask her if she is open to advice, and if she is, give some of your opinion and advice to help and support in a non judgmental way.

Also you asked if something more is going on with her. Maybe. I don't know. She could struggle w low self worth, anger, and sure, BPD. But I'm not a doctor and its important to recognize that no matter what's going on with her, whether BPD or just anger and emotional immaturity, she's a hurting person who deserves respect. Her anger may be disproportionate to the situation in your opinion, but instead of judging her, know that it sounds like she struggles with managing emotions and does not know how to deal constructively. That doesn't make her an awful person, though I get what you're saying about her being vidictive. That's imature. She is trying to make herself feel better in an unhealthy way. She may make things worse for herself if she acts on it.

She may need to see a counselor. What have you been doing to help so far?

You're a good friend to want to support her. She does sound a bit off putting. Just don't tell her that lol.