Hi Shannon! I can't think of a more magical place to celebrate a birthday than Walt Disney World. Guests often celebrate birthdays, or "un-birthdays" all the time, so yes, please use your time at Walt Disney World to enjoy an early celebration for your daughter. Please make sure you get your daughter a "Happy Birthday" button from any Guest Services location on Disney property. This button is sure to get her lots of smiles, and maybe even a few pixie-dusted surprises during your trip.
Since you are traveling in October have you thought about a very merry "un-birthday" party at one of my favorite hard-ticketed events,
Mickey's Not So Scary Halloween Party? This party will run select nights from September through October, and does require a separate ticket, but boy is it so much fun! During the party you will find special character meet and greets, a Halloween themed fireworks display, and probably one of the best parades you will ever see, Mickey's "Boo-to-You "Halloween Parade. It is a Not-So-Scary good time for the whole family.
Shannon, I would love to continue to help you plan an amazing "un-birthday" vacation for your daughter. Please let me know if I can help you create any other magical moments, it is my favorite thing to do.
Dream as Dreamers Do,
~Jen