Hi Renea,
You are doing the best thing to make it a memorable trip, starting ahead of time and planning. If you have not done so yet, check out
www.disneyworld.com, www.allears.net or purchase a travel planning guide. These are all great ways to see how many different things there are to enjy at Disney World. There is no way you can do everything, so it is important to pick a few things at each park, each day and start with those. Don't make your list to long, as the stress of trying to run to everything will take away from the fun.
Given your daughter's age, focus on Magic Kingdom first. This park offers the largest number of attractions that the whole family can enjoy together without age or height requirements, The park is the heart of Disney to most, and it is here that you daughter will find the greatest number of Disney characters & rides that are familiar to her. Fantasyland is the perfect place to visit and be sure to check out Playhouse Disney at Hollywood Studios.
You may find that she has the best times dancing down Main Street with a balloon, or playing in the fountains near Ariel's Grotto. If she is comfortable with the characters, be sure to plan plenty of time for autographs and photos at all the meet and greets. The most important thing at her age is to go her pace. Do not try and overwhelm her with to much. The best memories are the ones that come naturally. My favorite memory is the sight of my boys lying in the middle of the Beach Club lobby playing cars and Chip and Dale sneaking up to lay down and play with them. If we had been in a hurry to race to an attraction we would never have had this memory.
Enjoy!