I don't blame one incident on a whole disorder, there are many things she has done as well. She will do one thing that seems very caring, and then say something rather malice, like that someone has said something really awful about me, that has then turned out to be not even remotely true.
I don't want to offend anyone here in any way and make people with BPD sound bad, yes I'm sure I just have a poor understanding of BPD. I do know a little bit about BPD, but I don't understand it too well to know if having BPD 'causes', for want of a better term, someone to do certain things. I wasn't sure if she did it out of spite or jealousy, or if there was more to it. Not just this incident I guess, but other things she's done too.
I'd talk to her about it and have brought it up as I've said, she doesn't have much to say on the subject.