I doubt she'll hate you. If she does, it would be a better reason to leave than having a sad face. It does sound like you've got some extra loaded feelings about it, with the reference to her many clients.

There's a good chance that her face was telling the truth, but you won't know until you work it out with her.

I saw a therapist who made over-exaggerated expressions that I could not even look at. I thought of stopdog and the one she sees and wondered if they went to the same school. I did not see her a second time. It was creepy.

I think you can tell when it's genuine and when it's a reaction to being seen.