It is because YOU are bringing something to the relationship that she finds intolerable, scary, weird............fill in the blank.
What if she wanted to dress as a baby and act like a baby--would that be okay for you?
Or, what if she wanted to dress like a man and act like a man. Wear men's clothes (yea yea, I know some thing we already do), stop shaving, stop wearing makeup, cut her hair short, walk like a man, try and talk like a man.
Kew