Annie's Mind, that's harsh to hear that "no value" phrase.

I'm so sorry. I wonder what "value" telling you your letter had "no value" served to your T? Maybe she thinks she can force you to trust her?
With my T, there were things I could not talk about at first, and we just had to work on building trust by talking about things not so difficult. You know, get to know each other, trust him with small things and see he handled them well, did prove trustworthy, etc. Then I could gradually trust him with some of the "biggies." I see our early sessions as kind of like going through boot camp together, to get to a place where we can work together with trust and understanding. I remember once when I was having difficulty telling him something, he said "I respect your ambivalence about telling me" and that made me feel it was OK and even "normal" to have that kind of trouble in therapy. It helped me in later situations with him to move forward and share. Another time he asked me "what can I do to make it safer for you here?" And I thought of some things. Just his concern to make it a safe place for me made me trust him more. If he had read an e-mail I wrote and told me it had "no value", our relationship might have been irrevocably harmed. But, maybe that's just me--I have issues with stuff like that.
You asked, "Could it be that some of us are just no able/ready to be in therapy?" I think that is a great question to discuss with your T. Maybe that would be less difficult to discuss than something more personal. I know my first counselor always told me that if she didn't think I should be there with her, she would tell me, and that provided some reassurance I wasn't wasting her and my time. Maybe now that you have written her the email, you could even open the conversation with "I'd like to discuss that email"--that's easier to say than actually naming all the issues. And then maybe add, "it's hard for me, can you help?"
((((((hugs))))))
sunny