Who is Zannah from March and what is their importance?

Zannah is one of March's best students despite the fact that she is unable to speak. When she was a teenager, Zannah was brutally raped by a gand of men who cut out her tongue to prevent her talking about it afterward. After Oak Landing is attacked, Zannah saves March's life when she brings him to the Union doctors at great risk to herself. Unable to convet March's identity, she writes the doctors a note on the headscarf March once gave her.