This app was mentioned in 3 comments, with an average of 1.33 upvotes
This one is just called Solitaire Suite or something generic like that. It's basic but has 150+ solitaire games. Add are in between games and not annoying (you can x out immediately). Been using it for years. https://play.google.com/store/apps/details?id=com.rikkigames.solsuite
I highly recommend Solitaire Suite, if your grandma wants variety instead of just a basic few versions.
There are unobtrusive banner ads, and a 1.99 iap to remove them.
Also you can pay $5 to unlock all of the solitaire games at once, but you start out with quite a few, and unlock the rest through gameplay, which I find part of the fun.
https://play.google.com/store/apps/details?id=com.rikkigames.solsuite
I use this one:
https://play.google.com/store/apps/details?id=com.rikkigames.solsuite
There is only a small unobtrusive banner ad at the bottom.
It has a ton of games that you get stars for beating so many times, so the completionist in me really likes it. Some of the games are incredibly difficult too.