Why do you have the add the "without my permission"? Why try to control something you cannot control?
Why not, tell her instead: "I'm fine with you taking what your psychiatrist has prescribed. I'm fine with you getting another opinion about your medicine if you think you're overmedicated. I'm not fine with your arbitrarily deciding to reduce your dosage or quit taking your medicine without the support of your doctors, and if such action should result in a return or worsening of your symptoms, I will not stay in the M."
If she is going to do it, she is going to do it, whether or not she has your "permission." I truly don't think that trying to control her and treating her like a child when it comes to her mental health will help her. Rather, disempowering her is likely to undermine her own efforts.
