I don't know the legal angle, but I think they should have informed you that you were being observed, instead of assuming you knew. Maybe look at it as an opportunity for growth. You saw the mirror and got uncomfortable. At that moment was the time to speak up. Ask questions, like what the hell is mirror here for? Am I in a zoo?

I think that a lot of us with mental issues feel less than and get embarrassed when we are in a questionable situation with a mental health professional. I look at it like this. If I was in my gynecologist office and they had a one way mirror I'd want to know what the hell was going on! I would also immediately put a stop to activities. No difference in a mental health setting. That's just my 2 cents, but then I'm a bit weird.