Hi Kate, One option would be to book Cinderella's Happily Ever After Dinner in the
1900 Park Fare restaurant (inside the Grand Floridian Resort & Spa). This is by hosted by Cinderella, Prince Charming other members of Cinderella's family. Prince Charming will visit your table, and spend a few moments chatting with your daughter. In addition, she'll be able to watch him dancing with Cinderella during dinner.
We have also seen Aladdin in Adventureland in the Magic Kingdom from time to time. Prince Naveen and Princess Tiana are currently greeting guests in Liberty Square in the Magic Kingdom. See:
HERE.
I'd recommend that you stop by the Guest Relations counter near the entrance to the Parks and ask them to check if any other Princes will be available for "Meet and Greets" that day. It changes daily, so you may just luck out.
Hope this helps and that you have a Magical vacation!
Kaylene