Hi, Catherine!
Great question!
Kids dress up as their favorite characters throughout Walt Disney World, and I wouldn't think that your 12-year-old would be the exception.
While adults dress up during certain special events such as Star Wars Weekends at Disney's Hollywood Studios or at Mickey's Not So Scary Halloween Party at Magic Kingdom, at other times, adult Guests are discouraged from dressing up to look exactly like a favorite character. Here's the policy from Walt Disney World's online Frequently Asked Questions: "Adult costumes or clothing that can be viewed as representative of an actual Disney character" are "not appropriate for the parks" Clearly, though, this will not apply to your 12-year-old.
Have a wonderful time celebrating your daughter's achievements as you tour Walt Disney World! If you'd like to add a little something special, take a look at some special surprises that can be created by
Disney Floral & Gifts. There are some extra-special items that you can have tucked into your room as you tour the parks, bringing an even bigger smile to your daughter's face when she sees it!
Send more questions as you think of them, Catherine; we love to help!