The Lions of Little Rock by Kristen Levine
It's August 1958 and the high schools in Little Rock aren't opening due to the recent battles regarding integration. Marlee Nisbett has her own battles to fight in middle school. She's so painfully quiet that everyone either thinks she's mute or tries to control her every move, like bossy Sally and cute JT who uses her for math homework. Then she meets the new girl, Liz, who not only helps Marlee find her voice, but also herself. Unfortunately, Liz is battling her own problems and one day, suddenly stops coming to school. When Marlee discovers the truth behind Liz's identity, she must decide what she truly stands for and how far she'll go to make her voice finally heard.