Oh, nobody quite spoils the kiddos like grandma!!! Here are some ideas for you:
* order a gift basket to be delivered upon arrival (check out
http://memoriesbybetsy.com/Memories by Betsy/Welcome.html, or
http://peggyssweetsandmore.com/) or make one yourself and ship to the resort
* make an appt at Bibbidy Boppity Boutique for a makeover -- you can go so far as to include a princess outfit too. This is fun to do before a princess character meal.
* check into some of the kids activities like pirate cruises, Disney girl tea, Alice in Wonderland Tea, etc.
* create character themed invitations for all of your character meals/Table Service meals on your computer and have them "mysteriously delivered" by tinkerbell.... put in the room on your way out and sprinkle w/glitter. You can also order a cake to be presented at your celebration restaurant.
* check out a horse and carriage ride at WL or one of the other resorts.
* along the tinkerbell idea, leave little gifts out each night, as if from Tinkerbell. Sprinkle glitter around them and some on these boards have even made teeny, tiny tink notes on their computers as well.
* surprise all w/tickets for Pirates and Princess Party,
MNSSHP or
MVMCP if they are on during your visit.
* whoop it up at the Hoop De Do Revue
* get tons of pictures with photopass photographers and then buy the CD as a super souvenier for the entire family.
However much or little you do, your DGD will have a fantastic birthday just being at WDW w/her family and awesome grandma!