Ah, I should've had more faith. This felt like a good-natured manga with some wish fulfillment involved too. The pretty girl being mean to her because she was fat once too, and eventually they'll get along is in line with what I was expecting. It's not quite the jousei "best friend is best girl" thing, but it's becoming more common than ridiculous bullies and mean girls who get put in their place. Which is nice.
Also her realizing that they sent a skinny kid to take her away so she just checks him and then falls on him fuckin' ruled.