you could teach her something technology based. usually at that age most grandparents don't understand technology so that's always a good thing to teach

if you knew how to knit I'd suggest that. my grandma knows how to crochet and I only knew knitting until I moved in with her. but I didn't even learn crochet from her (she can only make squares) I learned from YouTube but I forgot crochet even existed until I lived with her.