Hello Jaycee,
I bet your sister is just bursting with excitement for this amazing trip. My daughter is also 7 years old and we were just there this past summer. Here were her favorites and I hope your little sister will have just as much fun doing some of these. In Magic Kingdom, her absolute favorite has always been the Mad Tea Party (teacups). Following behind that would be meeting the princesses in Princess Fairytale Hall and Enchanted Tales with Belle. The Barnstormer and Big Thunder Mountain Railroad were also her very first "roller coaster" rides. Although, we didn't see it, but it will be brand new when you go is the
Festival of Fantasy parade. This sounds as if it will truly be an amazing parade with its new floats and awesome costumes.
Moving on to Epcot, Soarin' and Turtle Talk with Crush as tons of fun for all ages. She might also enjoy doing Agent P's World Showcase Adventure. While the older ones in the family enjoy the sights and sounds of the different countries, she can be "saving the world" in this interactive game. There is no additional cost to this as it is included in the price of admission.
At Disney's Animal Kingdom, there is yet another fun interactive experience called
Wilderness Explorers. This scavenger hunt type activity was, by far, my daughter's favorite thing of the entire trip. Not only did she get excited finding and collecting "badges" around the park, but she learned quite a bit, too! In Disney's Hollywood Studios, be sure to go to Toy Story Mania, Voyage of the Little Mermaid (show), and Muppet*Vision 3-D.
Have a magical time. It will be here before you can say "supercalifragilisticexpialidocious!"
~Allison L