Just be easy on her if she's not pulling out what you're looking for.
With this band, my guitarist wrote all the tunes then I came in and wrote the lyrics/melodies, so he's got this idea in his head of how he wants these songs to sound but has very little ability in demonstrating it while having no problem asking me to do 200 takes of practically the same thing so he can hear the magic take that only exists in his head.
It actually got to the point that our bassist put his foot down with him as well and said "Christ, just let the guy sing the fuckin' song he wrote. If you're going to modify every damn thing he's doing why don't YOU just write the parts and sing them?"
In reality, the performance she has in her head and the performance you have in yours are two different performances, you just got to find a way to get what you each want in it.