Can I ask my s/o not to visit a male gynecologist who happens to be her friend?
That's weird. Why don't you want her to visit her gynecologist?
I am concerned that she'll tell her male gynecologist everything about us.
You shouldn't be restricting her access to proper healthcare. There may be something concerning with her health that she needs to see them for and it could produce more health problems in the future if she doesn't take care of it now.
I don't care. I hate her, I feel like she can't keep secrets. This is a perfect way to punish her.
You shouldn't punish her especially with her health. Controlling a partner is wrong and the relationship will not work out.