Unfortunately we live in a rich society that makes you feel ugly if you don't have the perfect body dimensions. Only in rich countries do you have diseases like Anorexia or Bulimia.
Ok so how do you get beyond that with the wife that is conscience of her not so perfect body? You constantly tell her she is beautiful and never make mention about her areas that worry her. My wife is on the thin side (high metabolism) and would love to gain a few more pounds (yes most people would love to have that problem right!). However I know she is a bit conscience about how she looks in certain clothes. I am constantly telling her she is "cute" or I will walk by while she is in the bathtub and yell out "whew - your hot" and stuff like that. It goes a long way!
I am in your wife situation. My husband loves me and how I look...I know he does, but I can't shake how I feel about myself. It's just how I have always been. I've always had low self-esteem. I am currently dieting to try and help myself and I do feel better seeing the weight go down.
I make mention of myself all the time when I look at myself in the mirror. My husband doesn't like it and tells me I'm beautiful, but I can't see it myself. It's just something that needs to be worked with. Just keep doing what you are doing...tell her she is beautiful, that you love her, etc. She will feel good about herself through you.