I think the main joke here is that she is the size of a cow and should instead focus on not eating so damn much, but instead she is risking whatever health she remains so that she can pretend that she is just as healthy as a thin person. Same way that salad dodgers will "run" and act like it's some big accomplishment, when in reality, they are destroying their knees. I certainly wouldn't fault a human for doing something to improve their health.