Hi Martha,
Tiana's dress is particularly lovely. Your daughter has great taste!
While Disney princess dresses (including Tiana) are available nearly everywhere at Walt Disney World, the delivery situation you're looking for would be nearly impossible to arrange. Even
DisneyFlorist deliveries are not put into guest rooms prior to their arrival, but rather are delivered after check-in.
I do, however, have some suggestions. You could purchase a dress yourself in advance via
DisneyStore.com or another retailer and bring it with you to your hotel. This way you could give your daughter a wrapped box when you get to the hotel. If that seems like too much to pack, you could also give her a Disney Gift Card when you arrive with the intent to go on a Tiana shopping spree when you get to the parks. Disney Gift Cards are available at Disney Stores, most gift shops in the WDW parks and resorts, and at many grocery and discount stores throughout the US. For more information on the princess dress situation at WDW, you may want to head over to the independent website blog.touringplans.com. Search there for an article called "Everything You Ever Wanted to Know About Princess Dresses at Disney World."
Good luck with your planning. Please let us know what else we can do to help.