Wouldn't it scare the shit out of you to know that your prospects of mobility are tapering by the day? That your knees can't bend enough to complete a normal walk animation? All jokes aside, there has to be something seriously wrong with her, cognitively speaking. And I am not referring to the typical lolcow autism. There has to be a part of the brain that factors in reason that simply does not exist for her.
Aaaand after a quick google search, here's a short interesting passage that confirms that theory: In obese children, a region of the brain in charge of controlling impulsivity, called the orbitofrontal cortex, appears to be shrunken compared with that of lean children, ..., the smaller this brain region was, the more likely the adolescents were to eat impulsively, the researchers said.
In short, the fatter a person is, the more it damages those "self-restraint" parts of the brain. She and Chantal are essentially stuck in an endless loop of overeating and don't even realize it's happening.