With all due respect, the OP said he wanted to avoid character dining! :ROFLOL: Reading is power!
Anyway, a few suggestions I might make:
You might want to go to one of the higher end restaurants. They make more accomodations for special requests like a cake. Really, tastes are going to be key here, so any info you have regarding what she likes would be good.
I would suggest Narcoosee's if she likes Seafood. The location on the lagoon can't be beat or Citricos. I have found the GF is one of the nicest venues on property. Artist's Pointe and the WL is also top notch.
I also might suggest BlueZoo at the Dolphin. It's a really creative restaurant, and it breaks the Disney vibe a bit without leaving property (and a quick boat ride from MGM's main gate if you don't have a car with you).
Really, though, I think the best thing to do is pick something nice that she would like then call them ahead. Let them know when youa re coming, and make arrangements for making it special. I think you will find the restaurant staff at these locations to do their best to be accomodating, especially when you call ahead.