Hiya Terry!
Thank you so much for your question! I'm so excited to hear that you have a 'first trip' coming up! So much fun to be had, and magic to be experienced! Make sure you stop by City Hall at Magic Kingdom Park and pick up her "First Visit" button for her to wear around the park. It's always fun to be greeted by Cast Members that know you're celebrating a special vacation!
As for some must-dos for a 5 year old princess...I've done a bit of crowd sourcing for you to make sure I got a variety of opinions, so here goes! At Magic Kingdom Park--Fantasyland is going to be a BIG part of your vacation. You'll definitely spend a bit of time here. In specific, Prince Charming Regal Carrousel, Dumbo the Flying Elephant, Peter Pan's Flight, and
The Barnstormer. Also, meeting a princess or two at Princess Fairytale Hall is
always a must-do.
At Epcot you'll certainly want to check out Turtle Talk with Crush, as well as
The Seas with Nemo & Friends, Frozen Ever After and meeting Anna and Elsa at Royal Sommerhus.
Disney's Hollywood Studios is the home of
Disney Junior - Live On Stage! which is a HUGE hit for those Disney Junior fans, and For the First Time in Forever: A Frozen Sing-Along Celebration is another must for the Frozen fan!
If your princess is an animal lover like mine, she'll also enjoy Disney's Animal Kingdom Theme Park! Some great attractions there are Kilimanjaro Safaris, TriceraTop Spin, and Kali River Rapids.
Have a magical vacation!
Amanda