Hi Shannon,
Three is a great age to celebrate at Disney!
At 3, one of my daughters was obsessed with Mary Poppins,the other with princesses. If yours is a princess type, you might look at a princess meal at Cinderella's Royal Table at Magic Kingdom or Akerhaus Royal Banquet Hall at Epcot. There are lots of other
character dining options. We've celebrated many birthdays at Chef Mickey's in the Contemporary resort.
There are amply opportunities to meet characters and get their autographs in all the parks.
The Bibbidi Bobbidi Boutiques at Magic Kingdom and Downtown Disney transform children into princesses. You must be 3 to participate, so that might feel like a special a big-girl treat.
As for rides and attractions, my favorites for that age (or even my age) at the Magic Kingdom are Dumbo, it's a small world, Mickey's PhilHarmagic, Winnie the Pooh and the new Under the Sea -- Journey of the Little Mermaid.
At Disney's Hollywood Studios, look for the new Disney Junior -- Live on Stage! show featuring Sofia the First and other young friends, Toy Story Midway Mania!, Muppets*Vision 3D and the Honey I Shrunk the Kids Movie Set Adventure.
The Festival of the Lion King and Finding Nemo - The Musical shows at Animal Kingdom are awesome. And there are many activities at Epcot geared to young children, especially in Innoventions and in the pavilions of the World Showcase, where kids can make free souvenirs. My daughters have loved tasting new foods in the countries of Epcot since they were preschoolers.
Make sure you pick up a free Happy Birthday button for her at guest relations. Cast members often offer special treats or surprises to those wearing the buttons.
I hope you have a wonderful time. Let me know if I can answer any more questions.
Wilma