To answer the question in the title of this thread-no, I don't think that your second letter is instigating. I think that you are desperate for a damn answer, and I would feel the same way.
Whether you are borderline or not, the way that your therapist responds to you is crazy making. It would drive me crazy too.
Honestly, you poured your heart out in both letters. You mentioned that you read your letters to her in session and try to talk to her about them, but she either deflects, or looks off into space and says "yeah…right…." This is heartbreaking to hear about. No wonder this whole situation is causing you so much pain and getting you so riled up.
I know that this wasn't part of the purpose of your thread, but something jumped out at me. You wrote her a note in June 2013 that resulted in her BANNING you from session for three weeks? She PUNISHED you (the client) by taking away your sessions, banning you, shunning you?? WTF????
Ok, back to your question. No, in a normal-person universe, I don't think that your letter is instigating. I think there are issues that you really want to talk about and questions that you desperately want answers to. I think that you want closure. I think that you want off of this painful and crazy-making merry-go-round. However, in this universe that your T has you trapped in…I highly doubt it will lead to anything that feels helpful or healing.
I know that so many on here have recommended that you cut your losses and find a different T. I can also really understand your reasons for staying. I just wanted to say that I'm sorry that you're in a situation that is clearly so painful and frustrating right now. You deserve better.