Hi ShrinkPatient, and welcome to PC!
Here are my thoughts, which are mine - I'm no professional or anything. But I can relate a bit to some of what you say. Almost a year ago now, I left messages for my T which he never mentioned, and I left a couple of subsequent sessions in a bit of a rage about that. It was when I was finally able to tell him how disappointed I felt about the lack of any kind of response that my therapy really started to get productive. I would definitely recommend going there tomorrow and just tell her. Say "T, I am angry with you for not reading the email I left for you, and I was full of rage about that on Monday, and I was not able to talk about it. It's very important to me that you read what I have written, because it is so difficult for me to open up in session."
Or something like that. I don't think you should go in and try to forget about Monday, I think you should go in and work out what happened.

Maybe her reaction will be disappointing. I very much hope that it won't be, that you'll be able to improve your therapeutic relationship through this.

Oh, and I see my T twice a week as well.