When I thought about what features I would like in such a game, it occured to me that I simply wouldn't play it on the computer. In some respects I really fancy paper, and I just would not play such a game for more than five minutes on a computer, whereas I could spend hours solving puzzles with pen and paper.
In your place, I would first off make sure that your mother would play that game on a computer.
Just a thought, though.