she's already explained that she's with that guy cos he snatched her when she was fat.
simple as that. she was fat and he was nice to her and her fat self-image is also why she's so funny.
she doesn't think she's hot, she sees herself as a fat chick who gave up caring about looks a long time ago. the dude is probably hell nice. we could all learn something from this, that fat chicks can turn out to be hot and smart and funny.