I know you asked about a girl, but I'm not sure why the answer would be gender-dependent so I will contribute based upon what my son liked at that age.
- Splash area
- character meets
- shows
- kids club during open house
- Wake up with Disney Junior
- Dancing to the live bands after dinner
- Looking out the portholes around the ship
- Being fussed over by everyone in the crew
We had requests to "go back on Mickey boat" for weeks after our trip ended.