Puddin' by Julie Murphy
It is a companion novel to Dumplin'. Millie Michalchuk has gone to fat camp every year since she was a girl. Not this year. This year she has new plans to chase her secret dream — and to kiss her crush. Callie Reyes is the pretty girl who is next in line for dance team captain and has the popular boyfriend. But when it comes to other girls, she’s more frenemy than friend. When circumstances bring the girls together over the course of a semester, they will surprise everyone (especially themselves) by realizing they might have more in common than they ever imagined.
Review from School Library Journal:
On the heels of her success in the Miss Clover City pageant, Millie Michalchuk is determined to pursue her dream of broadcast journalism and not let her weight define her life. Callie Reyes is the pretty and popular queen bee who is better at having useful frenemies than actual friends. When Callie's revenge prank spirals out of control, it destroys the image that she's cultivated for herself and leaves her working side by side with Millie. As the girls get to know each other beyond superficial impressions, their very different strengths push both girls toward what will make them truly happy. Full of humor and heart, fans of Dumplin' will not be disappointed by this book that builds nicely on the themes of self-confidence and self-acceptance without falling into lecture. This is a highly character-driven book and the authentically complex characters are up to the task. Not only is Murphy capable of taking both the popular and unpopular girl beyond tropes, but Millie is a starkly different character than Dumplin's Willowdean. Though very different, they believably find common ground fighting the superficial boxes teenagers often find themselves in and examining the defenses they've built to survive them.