Well what she should take from his eating crap is that some people can eat that stuff and not become obese so that means that EVERYONE shouldn't have to suffer because of someone's screwed up fat genes.
I don't give a crap what anyone eats. If they want to look like tubs of cottage cheese so be it. Leave everyone's food alone! 
No two people even siblings have the same metabolic process.
Family's with 2+ kids will find one kid is big boned, the other very small boned. Both kids small boned but one will have some kind of food allergy, big boned kids and one may find one of these kids grows up to be thin, the other well fleshed.
Since when is one size fits all, all diets fit everyone. Some kids may need more protine, another more carbos.
Everyone is different, kids that are sedentary may be thin, kids that get exercise through sports and on a diet still stay over weight.
Kids sent to fat camp for the summer never loose 30 lbs in 2 months,[ I hope] some kids are solid mussel and be considered over weight by their height size. When put on a diet they do not loose fat, they loose mussel----not a good thing.
All people. adults and children cannot be healthy on the same diet, those over weight need to cut down on the Size of their servings, those too thin need to up the size of their meals.
The body knows what it needs unless there is a health issue. I believe this is the reason we get cravings for bacon-fat, greens-vitimins- icecream-calicum.
I don't know what to think about the 600 pound people that are bed bound. Someone is feeding these poor people, this now gives the question of why anyone would as a care giver allow this and sanction the death dealing needs of the Patient.
I questioned why a neighbor that was around 200 pounds that had two daughters 8-10 years old and both girls were huge. I visited them one day and Mom was cooking lunch, hotdogs and Mayo.
Blew my mind, she was turning her girls into mini-her, to look like her, eat like her and give the excuse this was genetic. I thought that if her girls were thin then people would think she was a fat pig, but with her girls so big she could feel this was a medical problem the family had.
Crap people are people, no telling what they will allow their kids to eat or themselves.
