For some reason women are more fixated on their own bodies sexually than men. Recent studies have shown that women with very high sex drives will usually demonstrate some tendencies towards bisexuality for this reason. When women walk into a room they generally check out the appearance of the other women first before looking at the men. Heterosexual men generally check out the women before the men too.
So, IMO, there are three ways around poor body image causing low sex drive in a woman. She either need to learn to love her body imperfect as it may be or she needs to learn to love your body by increasing her sexual object-orientation towards the male body or she needs to concentrate on sexual context or vibe rather than any visual arousal signals.
So, it's pretty obvious that in terms of getting her to love her own body you are limited to offering validation and encouraging her to take action that might help, like increasing physical activity or getting in touch with her body in a tactile way through massage. However, you can try to create a sexual vibe that will take the focus off her body as object and put it either on your body or your masculinity. For instance, to take it to a ridiculous extreme, you could make her a bowl of popcorn and while she sits in a chair fully dressed you could perform a Chippendale's routine for her. Any sort of assertive throwdown will also be helpful in distracting her from body image problems because she won't have time to think about them.
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver