I think you crossed a line. It's ine thing to want to vet your T, check her registration, or to be curious about easily available info. It's another when you start crossing checking and making links to other people in her life and following them up. For you then to use what you knew as sources for your fictional writing and to use this to bait her is awful. Imagine if it happened to you, that someone found out intimate details of your life and used them in fictional writing. The other thing for me is that she is the person you have a relationship so some might say her online presence is fair game, but the other people in her life deserve privacy, her ex partner certainly didn't sign up for someone digging about in the intimate details of his life and certainly not for you to use his challenges for your own ends.

It's one thing to have a bit of information but I can imagine she's questioning how you know such very personal stuff, not just about her but people who are close to her. You wanted her to feel as powerless as you in the therapy room, I'm guessing she actually feels unsafe in every area of her life because she doesn't know what you know or how you know it. If you wanted to sabotage your therapy, you've done a good job of it.

I can understand you wanting to even up the power dynamic in therapy but to want her to feel powerless isn't ok, she's just doing the job you asked her to do when you started seeing her. Therapy doesn't always feel comfortable, we do feel vulnerable and sometimes powerless. The way to resolve this is to talk about it in therapy with your therapist. If I were you, hard as it will be, is return to the next session and explain all of it - your opening post would be a good way of starting - clear the air and see what can be salvaged. I don't judge you for doing it, I know you were trying to keep yourself safe, but my goodness if you want to continue in therapy with her you'll need to own your part in undermining the relationship.