Bad Best Friend by Rachel Vail

 Niki and Ava have the perfect friendship and both are eager to start eighth grade. Then the gym teacher asks the class to pair up--pick your best friend-- and Ava turns to one of "the cool kids," Britanny, and Nikki is devastated. Nikki has to decide who her real friends are. Meanwhile, life at home is complicated. Niki's nine-year-old brother Danny continues to act out more and more publicly. Their mother refuses to admit that Danny is somewhere on the autism spectrum, but it's clear he needs help. Niki doesn't want to be like her brother, to be labeled as different. She just wants to be popular! Is she a bad sister and a bad best friend?