A grandmother called her daughter after recently viewing a Facebook video of her granddaughter being assaulted by three other girls back in July.
That led the mother of the victim to contact Buffalo police on Friday and file gang assault charges on behalf of her daughter.
One of the attackers in the video was a student at the victim's school, according to the family.
The afternoon attack occurred near the intersection of Madison and Clinton streets, according to the complaint.
The victim suffered a bloody lip and pain to her back and lower body. An investigation is pending, police said.