My mother was never interested in games beyond a game we used to have for ColecoVision called "Ladybug." She could never coordinate well with conventional joysticks and controllers, it was just a foreign concept to her. That is until I showed her a Nintendo DS and the Brain Age and Crossword puzzle games. The concept of a touch screen, something she could physically manipulate, clicked instantly for her.
She's in her 60s, she doesn't comprehend the typical action game (she said it herself) so I would recommend Brain Age and whatever kind of crossword games there are to buy... and a gambling game, maybe something with the Caesar's Palace name on it, she loves to gamble.