If you can get all of the grandkids together for a picture I am sure she would think that is the greatest thing. Or of the grandkids are scattered about have them send (email) picture of themselves with their families and make up a brag book for her.
Does she have any needs or anything in particular that she complains about? My great grandmother used to always complain about being cold so one Christmas I bought her some cotton sweat suits and she loved them. I know it sounds cheap but she appreciated the fact that I had listened to her and tried to help her more than anything else I could have done.
First get her a desirable card, & have all your family members write, from their hearts in it. You should write a poem. Buy one single rose (white). Then her fav box of yummy soft chocs. Have her hang with you all for the day. She will sooooo love it.