My husband's solution to this problem was to ask me what I think I need to do to change what I don't like about my physical appearance, and then encourage me to do so. My anniversary present was an elliptical machine, like I asked for.
You really can't do anything to make her feel better about herself. We all think we're fat. We all think we're less attractive than the bartender that flirts with you for tips. We all know you'll probably say anything to make us feel better so you still get laid.
It's up to us to change our own opinions about ourselves and if we don't work at it we have no right to bitch about it. We have to either embrace what we don't like or do something about it.