I'ld have a problem with her using the word "tantrum." Sounds like she was releasing some pent up resentment . . . like she sees you as willful and has been wanting to voice that, even prior to this exchange.

I can't draw big conclusions on just this info. But therapists can be out of line, as can anyone. It's not wrong to practice assertiveness in the therapist's office. I'ld probably come right out and say that I don't find it constructive to be talked down to. Then I'ld ask her if there is some larger issue she'ld like to address.

If she can't even consider that she may have mishandled the exchange, then she may be a very willful person, herself. Therapy that descends into a war of wills probably isn't going anywhere productive.