Who is Rosa from The Fifth Sacred Thing and what is their importance?

Rosa is a young resident of San Francisco, Rosa is interested in studying music, and despite Bird's feeling as though his musical abilities have been taken from him due to the physical injuries he sustained in prison, Rosa becomes his piano student. She leads the children in a protest against the troops when the river is damned in Chapter 24 and is subsequently taken into custody with Bird. She is raped and is used to manipulate Bird during his interrogation.