Firstly she might think shes "fat" because shes with someone who reffers to bigger women, as "fat whales". Exactly how old are you? If she isnt happy with her weight then ask her n.I.C.E.L.Y to do something about it. And if u think shes fine the way she is then tell her that! Dont offend her of corse because in this day and age girls worry about their weight because everyone is anorexic these days, its kinda the same thing as a guy with a little penis feeling inadiquite to a guy with a larger penis.

I tell her all the time I think shes beautiful and she doesnt seem to buy it.

Im 29 by the way and I would never bad mouth her. In fact, I think a little belly is sexy.

Sometimes girls need to hear they are more than beautiful, do something nice for her like send her flowers or a sweet txt? And if u think a little belly is sexy tell her. Just dont say "i think a fat belly is sexy" cuz that will make her think shes fat! With weight you have to chose words wisely. Good luck mate