I don't know why the focus is on Linux.
I got a Microsoft Surface (rt) for my Mom and she loves the thing. It gets a lot of negative press for not being a "real" windows but it fits her needs well (web, email, Netflix, solitaire), has a touch screen and keyboard. It's relatively inexpensive and moreover, Microsoft offers two years of training for $99 (one lesson per week). You can't beat that price if your grandma is interested in learning more about her computer (assuming she's somewhat close to a Microsoft Store).