I'm glad to hear you set one up!

Perhaps you could start with "The reason it took me a while to contact you wasn't because I didn't feel I needed a session, it was that I felt [confused / hurt / worried] when you didn't get back to me about scheduling."

Regarding what she said, that she doesn't know what you get out of seeing her, it might be useful to simply tell her what you get from it, and that it's important to you. It would be a way of bringing that up, because that was an odd thing for her to say, but hopefully it would also motivate her not to drop the ball on scheduling in the future!