If she is the non get off her ass type of woman, changing her lifestyle will be difficult. My mother ( 60 ) recently started seeing personal trainer at 24 hour fitness, and it has worked out well for her. Most Women don't like being told what to do by their husbands, getting an outsider to train her might be a better option, as they will respond better to their pushing. If you push her all it does is make her resent you, and thus you get no sex for a while. But like what was said earlier,
Hard Work + treadmill + nutrition = Not Fat ASS.