Carol Costello, 69, was leaving a Daytona Beach Wal-Mart when a car blocked her way and a passenger with a gun jumped onto the hood of her car, The Orlando Sentinel reported Saturday.
The potential robber smashed a large hole in the windshield of Costello's car with the gun, which fell from his hand and landed in Costello's lap, the newspaper said.
She pointed it at the assailant, who fled back to his car.
As the alleged robbers' car drove away, Costello was able to write down its license plate number.
The would-be robber also dropped his cellphone, which included photographs that allowed Costello to identify him to police.
Police have identified the alleged robber as Raymond Lewis Shepard, 25, of Daytona Beach, the Sentinel reported.
The driver of the car has not been identified, police said.