Hi Jennifer!
What a great way to celebrate a special birthday - at Walt Disney World!
First of all, make sure you tell EVERYONE, from the Cast Member checking you in at your Resort, to the waiters serving you at the restaurants, about the birthday. You never know what kind of Disney Magic they'll send your way!
Thought I can't guarantee a balloon, they will usually have a special birthday button for the birthday girl. If she will wear this everywhere she goes, she is sure to receive sprinkles of Pixie Dust from Cast Members and even other guests wherever she goes!
Again, there is no guarantee that she will receive special treats such as a balloon, but it can happen, and happens often!
For some other ideas of how to celebrate the special day at Walt Disney World, visit this webpage:
Customize Your Celebration.
I hope you all have a wonderful time full of special surprises!