Really curious to know how big your wife is so I can judge whether or not you (and she) are being hypercritical or if she is a bit overweight, etc. I know that sounds assholey but it really makes a difference on the kind of advice people can give because depending on your answer, a good solution (to working up to rebuilding her confidence) could be you lower your standards cause their unrealistic, helping her with diet and exercise, or seeking some kind of cosmetic surgery to take care of lose skin, damaged muscles, whatever.

If you can help in any of those ways, whichever are applicable, you need to. And be a bit subtle. Do the diet/gym with her. Ask her next time she brings it up how she wants you guys to attack this issue as a couple (don't suggest cosmetic surgery upfront obviously) and work from there.