if she doesn't eat much then spilt something with someone else. most places are strict about the kids menu. you can call them and ask them if there are restrictions. but i say, if your going to disney, go all out.
you get a ton of food at RFC, husband and i easily split or as an alternative maybe she can get an appe and a salad or something. we got a crab dip appe that was huge! probably plenty for a lighter lunch
Well how old does she look? You could always just order the food as if she were 12 and if they ask any questions you could say she is 12. Not sure though because I don't know how old she looks.