Who is your DD's favorite character? Schedule a character meal so she is guaranteed to meet her favorite(s). It is expensive, but the character meals are very special for little ones.
And/or get FPs for required characters. Children get very disappointed when they have their heart set on meeting a character but the line is too long or you miss the meet and greet times. To me, the worst lines are the character lines. They move slowly and don't offer much by way of a queue (some lines are actually interesting to be in).
Having the Disney app on your smart phone is really important. It can tell you where nearby restrooms are, what is available to eat nearby, wait times for rides, and of course, maps. I also think it is a good idea to study maps of the parks you will visit before you go. When you already know where the key rides/characters/shows/restaurants are, you get less frustrated in the parks and waste less time trying to find your way around.
My DDs are 2 and 8, and they both prefer parades and shows to rides (although of course, we do lots of rides, too). Be sure to schedule time to see the parades, live shows, and fireworks.