So I had never heard of such a thing, but per Google grandmother showers are definitely a thing now. My mom's girlfriends are throwing her one. Which is super sweet and cute. I think it's more of a brunch/chance for them to hang out, but I'm pretty sure presents are involved too.
Re: Grandmother Shower
This thread inspired me to order two grandma books, one with each grandma name (neither his mom nor mine are called "grandma," so I was pretty happy to find an "Oma" book, for example).
Also went ahead and got a grandpa book for my dad and a dad book for my husband (for Father's Day, I guess). I'm pretty excited about giving these presents soon!