My current therapist had an intake questionnaire which focussed on 'getting to know you' conversational questions: there wasn't an expectation that I would need to prepare anything in advance.

It was immediately clear to me that she was warm and personable - for this reason, the article linked above resonated with me a lot.

I don't feel that I have any more ability to explain the state of my mental health than I did at the start of the sessions, but I'd definitely credit her with improving it.

To reflect on what you have said: If you ask me how my mental health has improved, I genuinely don't know. I just know that it has.