Well, I can take a crack at this with an example.
This happened some years ago. We had a new GG who happened to have weighed more than her husband. She said she was jealous of the way he looked while dressed. She felt he looked better than her and this made her feel insecure. I asked her if she also felt insecure when she was standing next to a GG who was taller and skinnier than her. She thought about it and then agreed this was the case as well. I further asked her, if she also took an hour to do her hair, apply makeup, put on a cute outfit with new shoes and nice jewelry, would she still believe her husband looked better than her. She finally relaxed and said, "Alsolutely not". She then came to the conclusion it was not her husband that she was jealous of, it had to do with insecurities about her own body image.
The concept of a husband who enjoys presenting as the same gender as his wife is in a completely new realm to many GGs and they need to sort through their own feelings, they need to develop a whole new way of looking at themselves and their relationships, before they can pinpoint exactly what is bothering them. You'll seldom find a GG who is accustomed to the idea that her husband dresses, say that she is jealous of him. You'll never find a GG who is comfortable with her body image (no matter her weight or height), who will say she is jealous of her husband.
If it is strictly a matter of weight or height, then this is a different matter. After I had my kids, I resented that my ex seemingly used to be able to eat anything he wanted, while I felt I couldn't indulge in that banana split if I wanted to lose the post-pregnancy bulge. But something like this is a far removal from believing that a husband fundamentally looks "better than a GG".
I hope this helps.