The girl became the 12th youth to be fatally shot in St. Louis since April, the St. Louis Post-Dispatch reported.
Those injured Friday night near Soldan High School in St. Louis were a woman in her 40s and two teenage boys, FOX 2 of St. Louis reported.
The girl had attended the jamboree with her family, according to the Post-Dispatch. Multiple fights broke out at the event, which police canceled around 8:15 p.m., the newspaper reported.
The gunfire broke out after police believed they had cleared the area, FOX 2 reported.
Around the same time, police responded to a report of a shot fired at Parkway North High School about 12 miles away during another jamboree, FOX 2 of St. Louis reported. There were no reports of anyone being wounded.