The attack happened June 2 at a park in Sauk Village.
Investigators say several girls beat and burned 17-year-old Mercedes Michaels and cut off her hair.
A 15-year-old from Crete and a 16-year-old girl from Steger have been charged with aggravated battery. They're under home confinement.
Two other girls, Sarah Kraft and Marcelena Castillo, are charged as adults in the case.
Police are still looking for the person who videotaped the beating.
