Mike, your wife has to want to make a lifestyle change. I have worked in an all women's gym and know women with very similar mindsets. I got to the point where I just wrote off any woman that wasn't into weights.
I train hard with weights. Normally 2-3 sessions a week with compound exercises, heavy weights, mid range reps (ie I would dead lift 12 reps at 60kg, squat and lunge around 40-50kg at 12 reps) and also do plyometric exercises.
I mix up my cardio- slow burn combined and interval training. I'm fairly fit, so I can run and keep my heart rate low for slow burn, but at first it would mean a long walk for about an hour until interval training increased fitness levels. I also find it limits injury when you mix it up- have a pretty battered body and find it helps.
Tell her to go and look at all of the pudgy women that do heaps of spin classes. Sure, might have cardio fitness, but still have a spare tyre and chicken wings!