Oh, another thing to keep in mind:

Your mom can (and probably will) say whatever she wants to and say it's from your therapist. Based on the other things that it seems like she says, don't put it past her to pretend to know things he's "said" to her.

Talk to the T specifically about all of this when you see them next. Find out what forms you have signed - what is your confidentiality like. Ask him directly if he is allowed to talk to your mom, and if he says "yes" then you can revoke that permission. Ask him about everything that your mom has said to him that you've heard.