"I'm not going to cancel all our future appointments." You don't have to say why. If she asks, you can keep it vague and just say "I don't think we're a good fit," or if you want you can give a little more detail and say something like "we have very different perspectives on mental health--mine specifically--and I'd rather go with something that makes more sense to me...(given all the information I've gathered from the [insert however many years old you are here] years I've been using this brain)" (you don't have to add that parenthetical if you don't want to come across as "smarter than her" in anyway if she has a "I have a paper saying I know more than you so your words are invalid" attitude. That little tidbit might leave a sour taste. Some therapists...some...are open to the idea of "hey, maybe this person knows more about themselves, their past, and how it affects them than me." but I don't think your T is the case if every one of everybody's mental health struggles are caused by trauma.