Take this advice. We as seasoned gamers probably take a lot of our skills for-granted and already know what our preferred genres are. We already sorta know if we will like something if we hear and see a bit about the game. You kinda have to take a step back and break down the elements of the game you are looking at and see what a newcomer would think of it.
When I had to listen to my brother explain the controls for a guy starting to play Modern Warfare 2, I was amazed. (Right stick to look, left stick to move, click right stick to knife, right trigger to shoot, left bumper to aim, A to jump, B for stance, etc.) You have to take into account how multi-tasking intensive the game is, how many actions are assigned to each button, how many buttons you'll be expected to use commonly throughout the game or within a period of time, etc. You don't want her to be overwhelmed by the stuff you have to memorize and the things on the screen that you have to pay attention to.
Out of curiosity, how did she end up messing up Sonic 2? Is it really that hard?