Mary Knowlton, a librarian, died Tuesday evening after the accident in Punta Gorda on Florida's west coast, the police department said.
She was one of 35 people taking part in a two-hour course given by the so-called Citizen Police Academy.
Knowlton was one of two people selected randomly to role-play in a scenario in which they had to decide whether to use lethal force against a "bad guy" played by a police officer.
"I absolutely am devastated for everyone involved in this unimaginable event," police chief Tom Lewis said at a press conference.
The officer involved in the shooting has been placed on administrative leave pending an investigation.