That's called an eating disorder

Meaning you can't empathize? Lucky you, I guess. I had so much anxiety around eating for so long, and it's not unusual. Until I was 25, never put one piece of food in my mouth without thinking about the calories and how it would make me fat. I'm sure she looks in the mirror and still sees fat.

Yes more people have eating disorders in the other direction, and will eat when stressed. I have trouble wrapping my mind around that. It's been half my lifetime since I recovered but I still can't eat when stressed.

It's heartbreaking and eventually fatal if you keep restricting. Skinny is not automatically unhealthy, body types do differ.

There's plenty of pressure on women to be small, and when your life is out of control, one thing you can control is eating. It is oddly easy to fall into disordered territory.

Some people describe visual hallucinations as a component of body dysmorphia. Folks like this with serious eating disorders (like, going to kill themselves serious) are actually acting out of a delusion, not misinformed, rational thought.

Social pressures. Yes, being hungry is uncomfortable and even can hurt, but if you ignore it long enough, it can sometimes become a bit more like background noise. I have always been a healthy weight, but my entire life I have had the paranoia of becoming fat. And so I am very accustomed to feeling hungry. When they started me a psych med that people can easily gain weight on, I started monitoring my weight more closely. Often, I go to bed with hunger pangs.

Quite frankly, I never understood how people are able to eat as much as I see them eat and still maintain a normal weight. I have always needed to eat less than others to maintain a healthy weight. My coworkers will eat 3 meals a day and be a healthy weight, but I have to eat 1 regular meal, 1 small meal, and maybe 1 small snack to stay a health weight. I'm guessing it's because I'm shorter so there is less mass at a healthy weight. Sucks.

The whole thing about eating disorders is that no part of it is about enjoyment. Generally they're psychological/other issues that ends up skewing how the person views and interacts with food on a fundamental level.

It could be the pressure of 'staying pretty'
making them hate themselves for eating to the point of detriment. I understood that ozempic, the weight loss drug, is also widely used, which could be additional peer pressure.
These people are constantly scrutinised under a microscope, it's a lot to handle.

Obviously all speculations, there could be other reasons.