My guess would be since your mom was in on your first session, you may have singed a release of information (consent) for your therapist to talk to your mom at that session. Ask your T and see what she says. If she says you did, tell her you want to revoke that consent. If she says you didn't then tell her you are upset and ask to talk to her supervisor. If she works in private practice you can take the issue to the state licensing board.