The incident happened around 9:30 a.m. in the 500 block of Harrington Road in Havertown.
89-year-old George Metzger was behind the wheel of a beige Buick as his wife 85-year-old wife, Rose and 62-year-old daughter Gail waited to get into the vehicle.
Police say Metzger was preparing to back out of the driveway with his vehicle stopped and the transmission still in reverse.
Gail was trying to help Rose into the front passenger's seat when, police say, Metzger accidently stepped on the accelerator pedal causing the vehicle to travel backwards, knocking the two women to the ground.
Gail was flown to the Hospital of the University of Pennsylvania with serious injuries after being struck in the chest. Action News learned Thursday morning that Gail died of her injuries. Rose was taken to HUP with moderate to severe injuries to her lower torso.
George Metzger was also taken to the hospital.
Police say this is being treated as an accident and no charges are expected.