You're right, that wasn't appropriate of her.

I will challenge you though on assuming she lost her cool because she's just worried about her reputation. It was pretty inappropriate for you to threaten to contact another client with the insinuation that you would say things to that client that would be disruptive to her therapy. I mean, I'm sure she was very angry based on the fact that the only reason you even had access to this client is because she was allowing you to come to group free of charge. Most people would be furious that such a gift would be twisted into a weapon. Again, not saying her conduct was justifiable AT ALL, but you need to look at your own part in this, as well. I also send angry texts to my therapist, but I would never threaten to interfere in another client's therapy. That is way over the line and I'm pretty surprised she didn't just terminate you.

Maybe you should check out the referral option and see what they have to offer since it sounds like your current therapist is not equipped to deal with what you're bringing to the table at this time.