i agree with the more sentimental, "home made" gifts that a few people suggested! it would be cool to burn a cd of some of the most popular songs throughout her lifetime.. i would love that if i were her, it would bring back memories and i'm sure there are songs that she hasn't heard for a while. what about pictures of her, are you able to get those from family/friends? maybe a picture of her from each time frame of each song, so that they sort of go along together? you could make that into the insert for the cd, if you have that sort of software (i used to have something like that). that would be awesome and i'm sure some of her family members would like a copy, too (i would of my grandma or great grandma's if someone did that for her).
OR if that is just a bit too much work, throw together the songs on the cd, take her out on a scenic road trip (if you two are that close and she is in good enough health/spirits) and play the cd while you're on the trip.. it doesn't even have to be far, even just local destinations i'm sure would still be awesome for her.
if you're not that close with her, i have no idea then.
but good luck!