She was initially being held on murder and weapons charges at the Essex County Juvenile Detention Center in Newark.
She was not identified because she is a juvenile.
Police say the girl immediately became the prime suspect after the body of 18-year-old Idresa Lightsey was found in the parking lot of the Otto Kretchmer Homes Sunday night.
Lightsey had been stabbed in the head and neck and was pronounced dead at the scene.
The body was unidentified for some 16 hours before a relative of Lightsey came forward. She was a former West Side High School student who hoped to someday attend college or join the Navy, the friend said.
Detectives have not found the murder weapon.
Witnesses believed the stabbing was over a boy.
