Authorities say the mother heard a popping sound late Wednesday, than turned around to see her daughter slumped over in the backseat.
Police tell WSB-TV that the girl was shot in the head. She was flown by helicopter to Children's Healthcare of Atlanta at Egleston. Her condition wasn't immediately known.
The gunfire happened near Georgia 54 and Fayetteville Road in the Jonesboro area.
Investigators Wednesday afternoon were working to determine the circumstances of the shooting.