Even with reassurance its difficult to accept that others dont think youre fat when you have that belief in your head. It takes some convincing and some repetition, try to be patient because shes had a lot of years of society convincing her she is. When she says it again, take her face in your hands, get her to look you in the eyes and say firmly, you are not fat and i’m sorry society made you feel like you are. You are healthy and sexy and i love you just as you are.