What wonderful grandparents you are! I know this cruise will create a lifetime of memories for your granddaughter.
As others have mentioned, there could be many reasons why you haven't seen kids in the dining rooms on your earlier cruises. Dwayne makes a great point about the early seating. This is when we take our son, as the late seating begins after what is his normal bedtime at home! Whatever you do, please take her to the dining room. It is a great experience, and the waiters will treat her as a princess. Enjoy!