What's wrong with my girlfriend?

my girlfriend is a great girl. she really is, but lately somethings been wrong. shes been very moody and intolerant of me, and i know it all stems from one thing. her low self esteem. shes honestly the most beaufitul thing ive ever set eyes on and i tell her that all the time but she cant seem to get it. shes soo self concious and thinks shes ugly. shes so concerened about her self and what she eats and all that that it gets in the way of our relationship, because she'll go into such a deep funk that she's just sad and cant even talk really. she knows theres something wrong w her, but also she wonders if somethings wrong with us..and from my point of view, nothings wrong. weve had a great relationship buy all this stuff is making it hard, and ive done what i can to help but nothing seems to work. i really just want to know how i can make things better for her, and for us. thanks