I think your T will understand that you weren't ready yet when you told her you forgot about it; most likely she doesn't really think you did forget about it, not if it came with such a storm of tears.
Others have said so many good things. All I really want to say is that it's OK to be afraid and it's very much a part of the process, but don't let the fear be something that keeps you from the healing you do need and deserve.
Things I didn't think I needed to process either have revealed themselves to have much more effect on me unconsciously than I was ever aware of before.....becoming aware of the need to process them is painful in itself, so I know fear well, and shame too in the struggle to talk about the past.
The effects of the past are in the emotional present, so the past hasn't really gone away.....there needs to processing, so there can be change and healing.