Hi, Megan! I would absolutely recommend the Magic Kingdom as one of the parks that you visit during your stay. There is plenty to do and see that even a child that age can participate in and enjoy, and there are also quite a few dining options within the park so you can spend the whole day there and not feel like you have to go elsewhere to grab a bite to eat.
I also think the Magic Kingdom offers the most in terms of the whole Walt Disney World fantasy experience - the parade, the fireworks, the characters - there really is a bit of everything there. You will forever remember the look on your daughter's face when she sees It's a Small World!
My other favorite option for children this age is Disney's Animal Kingdom. My girls at this age always loved the animals and the Festival of the Lion King stage show. The petting zoo is a big hit as well.
If you go to
www.disneyworld.com , you'll be able to check out some of the maps and attractions for all of the theme parks. That will help you decide what things are must do's for you and your daughter.
Have an absolutely wonderful time, Megan! I hope your daughter enjoys your vacation!