Y'know....
Even if she was looking at your page, how is that any different from all the people on here who look up their therapists and psychiatrists? Everyone gives them support for looking up their Ts, so maybe you should try to have a slightly kinder outlook towards your T.
Yes, she should have not been doing that. Yes, she should have sent a message saying that she made a mistake. Here's hoping that she will at least apologize and explain herself when you see her next.
But it doesn't have to mean that she was spying on you. It's no different than people looking up their Ts... it's just normal curiousity. I'd try to look at it like that until getting to talk to her.
((Side-note: if my T added me to his fb, we'd probably have mutual friends and I wouldn't mind at all - everything on my fb is "Niece-friendly"!))