Are you having a Wishes wedding? If so just use your comp night on your wedding night and stay somewhere else. Also, how do you know your grandma will be next door, did you request adjoining rooms?
My suggestion depends on where you are staying to begin with. I don't think you can go wrong with any of the deluxe resorts. How about staying at the Grand Floridian and then ordering room service and have an in room massage the next morning or go down to the spa. I also love the Wilderness Lodge. We honeymooned in the Royal Asante Presidential Suite at Animal Kingdom Lodge and it was fantastic!