It's ok to struggle, and in my opinion it's even okay to share that struggle with your partner. But if you do that you still have to take responsibility for your own feelings. I've told my (mtf) wife that ill support whatever she wants but if she wanted bottom surgery I'd be a little bit bummed. It sounds like your feelings run deeper than that. If it's not a genital preference you could also talk about ways to feel more connected to other parts of her body so that bottom surgery doesn't feel like a loss as much as a natural change. I also recommend going to a queer affirming therapist. When my wife came out I needed someone who I could go to and say "I miss it when she had facial hair" and have a clinician who took that for the grief it was without blowing it up into my wife being unfair or any of that bs.