Jennifer,
Here are the three you should consider;
Cinderella's Royal Table
This is the most famed and popular of all. Breakfast is still the hardest time to get, but dinner might be even more magical. This is expensive, but she gets to see many princesses, typically including Cinderella, Ariel, Snow White, Belle, and Sleeping Beauty. This is great because she stands a better chance of seeing one of her favorites with so many choices. Lunch is also an option here.
Akershus Royal Banquet Hall
A more affordable alternative, the princess choices are the same, and I think the in-dining interactivity is a bit more stepped up.The reviews of the food are hit-or-miss, though I have always had great meals there. Open for breakfast, lunch, and dinner. I prefer dinner, as that part of the Epcot park seems deserted in the morning.
1900 Park Fare
This character buffet dinner is all about Cinderella. If she is her favorite, this is the best choice, since Lady Tremaine, the wicked stepsisters, and others from that tale come to visit. If she is not exclusively gaga about Cinderella, the others might be better choices.
Please feel free to send me any follow-up questions from my bio page!
Have a magical (and delicious) vacation!