Hi Kayla,
Traveling with an eleven year old is going to be so much easier than with a two year old - you will have so much fun together!
At that age my kids enjoyed the trip a lot more when they were involved in the trip planning. There are lots of great Disney planning websites and books in the library. She could pick out some of the fun things she would like to do. She could also check out the calendars on www.disneyworld.com (under the
'Parks' tab, just pick the park you want to visit and then click 'Calendar' on the left side of the screen). On the calendar pages you can see the times of the parades, fireworks and special events. The two of you can have a ball planning your dream itinerary!
In mid March the days are usually lovely and warm, often in the 70's. Hats, sunscreen and water bottles are a must. But it could be cool in the evenings, so be ready with a sweater, light jacket and/or a rain jacket.
Kayla, have an amazing time planning your dream trip!