Some experience with BPD is helpful, but not necessary in my opinion. Therapy is about you and what this chaotic relationship brought out of you.
I agree with this. I was lucky, my T does work with pwBPD too, I did ask for someone who was experienced with BPD when I called around. I thought it would be easier if they had some experience. It's good, IMHO, that your T has some working knowledge of BPD. (I'm not sure if that's what your saying Take2, or that she doesn't have enough knowledge) About the 3rd session with mine I told her "BPD is HER issue, we need to talk more about MY issues." I got a thumbs up from her and we proceeded from there. There was a "why" I ended up in this relationship and stayed, more than one "why" I should add.