Well, my therapist replied, and I think her reply was good enough for me to find peace with, what do you all think? She wrote:

"Hi XXXXX, I just looked back over the e-mail thread in dispute and I am okay with charging you the standard fee on that one. I have not felt well this afternoon and not thinking at my best. I was tired and irritated with getting the e-mail reminders when I billed you; the $50 charge was automatic and not thoughtful. I will just credit your next e-mail session for the $15.00 if that is okay with you. I am available now for chat if it is something you need to discuss further, XXXXX"

I wrote her back a reply about why it bothered me, and asked her, in lieu of giving me a credit, to reply to that, and we'd call it even. I'm kinda mad, but... I hope it'll work out. I know that my stress level is super-high right now and I'm desperately tired, and that maybe this will seem like less of an issue if I get a few nights of good sleep. What do you all think?