You have a "problem of the beginner and the professional."
Professional different from the novice knowledge of the application area and the ability to organize their work. How well does your wife know graphics in games? Let him take a few games and try to make a copy of the drawings.
— Register for DA (http://www.deviantart.com/) and look there, repeat. And let them create their own gallery there.
— She needed a course of pencil drawing, to be controlled with a tablet. On rutrekere was simple but understandable rate
— It would be good to read at least one book on academic drawing.
— Try to draw every day.
— And when comprehend Zen let studying Gimp (I hope by the time released version 2.8).