Let her look. The issue isn't going to be what's easiest, but what she enjoys. Angry Birds is easy. There's little skill involved, but I don't play it cause I think it's stupid. There are some great space alien and 3rd party shooter games that are really easy - you suppose your mom wants to play those? Nah, probably not.
There are a ton of threads here recommending favorite games. It's now up to you to recommend she read those threads to get some idea of what she'd like. (Cause we really don't need one more thread recommending apps/games.)