OP, I see what you are getting at and I don't think you are cray, but I do think that asking her not to bring an iPad isn't something you have the right to do. You can, however, simply ask her not to bring it to the dinner table during the meal, or restrict the kids from using it even if grandma is.
If this is your biggest form of stress during the holidays, consider yourself very blessed!
You could always hide her iPad charger so that the battery goes dead...and then mysteriously sneak it into her bag when she is about to depart.
