latoya tilson , 33 , was reportedly hit in face during fight on saturday night .
she took out .25-caliber gun and fired several times into the feuding crowd .
but while one bullet struck a boy , 17 , other hit her 15-year-old son , pierre .
pierre rushed to hospital with gunshot wound to head ; he died on monday .
mother fled scene , but was later arrested at home in college park , georgia .
tilson was arrested on a number of charges , including aggravated assault .
charges will likely be updated following high school student 's tragic death .
pierre was ` trying to protect sister , 13 , from other boy when fight started '