Yes, the reassurance checking is often the compulsion. I would show her this video about the need to pee to help educate her:
And this one on reassurance seeking as a compulsion:
Also, reading books on OCD can be helpful. What to Do When Your Brain Gets Stuck and Practicing Being Brave are two good ones.
The goal would be to help her understand that her OCD is tricking her and making her doubt if she has peed and her asking grows that worry. You can do challenges where she goes a certain amount of time without asking for reassurance.
Regarding the self stimulating behaviors, the more you draw attention to it, often the more it grows. You can help her find some other self soothing behaviors and set boundaries (like you have been) for when it is not appropriate to do this behavior.