Hi Melissa,
With a 12 year old who thinks she is all grown up, i recommend visiting Disney's Hollywood Studios and Epcot first. If she likes thrill rides, then I definitely recommend visiting the Studios first. Once your daughter sees that Walt Disney World has attractions, shows, and experiences for all ages, then I recommend visiting the Magic Kingdom. The Magic Kingdom is the crown jewel of the Walt Disney World Resort and has attractions for all ages; I'm old (at least my kids tell me that) and it's my favorite place to be on Earth!
The World Showcase part of Epcot has some great places to shop and eat. I don't think you can go wrong with any of the Table Service restaurants in Epcot. Just be sure to make
Advanced Dining Reservations (ADRs). ADRs can be made up to 180 days in advance. Walt Disney World has some amazing places to eat, both inside and outside the theme parks; some of them book up very quickly. My personal favorites are Le Cellier Steakhouse in Epcot, Whispering Canyon Cafe in the Wilderness Lodge, Boma in the Animal Kingdom Lodge, and 'Ohana in the Polynesian Resort. A spectacular place to have dinner is the California Grill on top of Disney's Contemporary Resort. The food is fabulous and the views are fantastic, especially at night.
You can get more ideas on celebrating your daughter's birthday
here. If you really want to go all out then I recommend contacting a Dream Maker at Disney Floral & Gifts. They have done some absolutely amazing things in the past; they offer experiences at different price levels. A Dream Maker can be reached at (407) 827-3505.
Enjoy planning your trip and write back if you have any other questions!