I agree that your T sounds very kind and understanding. The fact that she still texted you to reassure you is a good sign.

I've shared feelings with my marriage counselor, and was afraid to come in the next session, but it was OK. The fact that you've had a long relationship with this T is encouraging. So you have a lot of history with her.

Could you send her a text or e-mail saying how nervous you are? Maybe her reassuring you more would help. I know how intense the feelings can be and how strong the fear can be, especially if you have issues with abandonment and/or rejection. But it sounds like she'll be understanding. If you get in there for the session, and it's too hard, just think that you could always leave. But I think you'll be OK, and it will be healing to face her and talk to her and see that she still accepts you.