I've seen my grandma last weekend and it was yet another reminder of how non intuitive technology can be. Whats-app asked her to rate a call she just had, and she was confused by it. She tried to read the message i sent her, but clicked my photo instead of my name, and therefore ended up on my profile instead of our conversations.
Our modern UIs really assume that the user will guess so many things. It's a bit of a shame. I think many grandma should be employed as usability testers for apps. We'd all get better software.