My T (who has 30 years of experience) says "I don't know" quite often and I think it often feels like it is about one of two things:

1) A reflection of the reality that we don't know very much about many things. As I've aged and become a real "expert" about my particularly intellectual area, I realize how much more nuanced many things are. "I don't know" is a an acknowledgement of how little we can know, especially about the future.

2) I am quite articulate verbally and often have the ability to make things sound more certain than they perhaps are. So sometimes I think that she is downplaying "facts" or certainties as a way of helping me be more open-minded.

I suppose what I would say to you is that you are interpreting her statements in a particular way that may or may not fit, or be right. Only way to know is to open the dialog with her and ask, "hey I've noticed you say 'I don't know' quite often. Why?"

On the writing, I resonate with what you've written. Writing about my experiences has been incredibly healing to me. Keep at it, is my advice.