I say you should totally do it. In fact, I did a similar thing when I first started t. I had so many things that I was and still am too shy/embarrassed to talk about and she was constantly encouraging me to try to allow her to shoulder some of the weight. So I finally broke and wrote her a letter telling her whatever my heart could allow - she called it a very open "naked" and vulnerable letter - it was 12/13 pages long typed. In the end, she knows whats going on and I know that when i'm comfortable broaching a topic in detail, she will be past the "shock" factor. It made things awkward (for me not her) but that ended up beginning the awesome relationship we developed.

I say go for it. Emotions are always more raw in a letter, and at present. It allows T to see things beyond the context of conversation in the room and more "in the moment". T will be able to see how things are in your mind and perspective (my T calls my letters "heart thoughts") and I imagine the next session would be very helpful for you and productive. Good luck on deciding!