"This is my health and I'm going to speak about this with a doctor. I love you and appreciate your perspective, but this is my decision to make. If any changes as a result of this impact you, we can discuss them, but I've made my decision and I expect you to respect it the same as I respect the decisions you make about your health."
The fact that she thinks she gets to decide what medications you get to take is nuts to me. This is a boundary it's very worth building and maintaining. If side effects impact her then you can negotiate, but it's your body. You have the autonomy to decide what happens to it. She's just a trusted advisor on the matter of your body.

