Hi there, Jessica!
Walt Disney World offers a world of fun for Guests of all ages! Make sure to pick up a complimentary birthday button for your daughter; these are available at your Walt Disney World Resort check-in desk and at any Guest Relations spot throughout the property. Do have her wear it for the duration of your visit!
Magic Kingdom is precisely where I would start, especially to celebrate a fifth birthday. I would consider actually making your Kingdom visit a two-day experience; this will allow you to tour the Park at a leisurely pace and will ensure that you will get in all of the rides that your little one has on her "must-do" list.
Additionally, having a second day will give your traveling party the freedom to head back to your hotel in the afternoon, should someone need a rest or a dip in the pool (a favorite escape of many during the warm Florida spring and summer months!).
On your third day, you can consider adding another Park - or heading over to Downtown Disney for some dining and shopping. There's always some kind of entertainment in the works, too, generally from the incredibly talented participants in
Disney's Performing Arts Onstage youth program.
Or take in a water Park! Both
Typhoon Lagoon and
Blizzard Beach will be ready for loads of splashing in the sun. Side note: for a little one, I would definitely recommend Typhoon Lagoon: lots of low-key body slides, a great kids' play area, and not as much climbing as Blizzard Beach.
Please let me know a little bit more about your preferences and I'd be glad to tailor my answer to you more specifically; just drop me a line when you can!
See you later, celebrator,
-Deborah B.