Im sorry this diagnosis has been so tough on you, it sounds as if it was a lot to go through.

As Moment said, your therapist hasn't been proven to have made a misdiagnosis. Two different professionals have had two different opinions, thats all.

DSM criteria are very broad and loose, and just about anything can be made to fit them or not fit them. It is down to a trained professional to make their own judgement based on experience. I'm guessing what your therapist meant when she says she doesn't really use the DSM criteria is that she uses her own experience which is far more complex and nuanced (but will always still be based on the criteria, just not in a straightforward black and white way). All psychiatrists/psychologists do this, otherwise any person off the street could make a diagnosis. If it was just a case of a simple ticklist, why would you need professional opinions at all? I see it as OK for her to diagnose based on her experience, then use the DSM code for official purposes.

Its also totally fine for you to disagree with her professional option and stop working with her. That is your right. But sorry to say, you wont get her to admit to a mistake because in her view she hasn't made one.