Sara,
I am right there with you! My girls, now 4 and 6, are in the same exact princess-crazed place!
So I find that while it is very expedient to see a lot of the princesses together at special meals, like at Cinderella's Royal Table and Restaurant Akershus, it is also nice to have more 1-on-1 encounters.
I would recommend that on days that you visit Epcot, for instance, that you ask cast members about when princess greetings might occur in that park. Meeting Jasmine in the Morocco pavilion or Belle in the France pavilion are really special, scenic moments.
Of course Jasmine in Adventureland over at Magic Kingdom is very nice too, as it is a similarly themed atmosphere. Another great 1-on-1 greeting in the Magic Kingdom is Rapunzel over by the castle.
But greetings are not everything. At Hollywood Studios I highly recommend the
Beauty and the Beast - Live on Stage show.
The Voyage of the Little Mermaid is also a
"Must Do!".
Finally, an overlooked character meal that might be perfect if she is a real Cinderella fan is the dinner at 1900 Park Fare. It brings so many more characters from that tale that it really makes for a magical meal.
Write me back if you have any follow-up questions from my bio page!
Have a magical vacation!