Hi Mereddy,
Happy almost birthday to your princess! Celebrating birthdays (ok, ANYTHING) at Walt Disney World is definitely the way to go!
You can certainly add some more magic to her birthday by setting up a private party at one of Disney's wonderful venues. You would be amazed at some of the things Disney's planners can dream up. My first piece of advice would be to look at
Disney Floral and Gifts website for celebration packages. These packages are incredible, fit any price point, and the best part? They'll deliver it to your resort room and set it up!
Keep in mind that you can order a specialty cake to be delivered to one of the restaurants on Disney property by calling Disney's Cake Ordering Hotline at 407-827-2253. I've been on the receiving end of those cakes a few times...they are so beautiful it hurt to cut into them, but I'm glad I did because they are delicious!! You'll need to give them a minimum of 72 hours notice before your arrival.
I'd also suggest you call 407-828-3318 to speak with a Castmember who specializes in coordinating Disney trips for large groups.
Disney Group Getaways is another site that you can look at for planning.
I hope this information helps, Mereddy. Wishing you and your family a magical vacation!