When things are calm for a moment, see if you can have a talk with her. Explain your side, that the wedding was something you never saw coming, really, and you know grandma and grandpa were there in spirit. Not everyone deals with surprise well. Then set some ground rules of what your schedules are and what she can expect while she's there, discuss any day trips, etc., and every time she gets mean and cranky, just think of her in your mind as a cranky three-year-old who needs a nap!