The day before Visiting Day, Tris realizes she's just too muscular to wear her old clothes. But when she goes into the dormitory wearing just a towel, she gets bullied by Peter, Molly, and Drew. Like, Peter grabs her towel away from her.
Luckily, in the training room, Tris gets a chance to fight against Molly. But since Tris has been studying Molly's fighting technique—and since Four gave her some useful advice about fighting in Chapter 11—Tris kicks her butt.
She doesn't feel bad about it at all. To be fair, neither do we, really.