The girl, identified as Diana Kadribasic, died on Sunday after she was hit by an R train at the 63rd Drive-Rego Park station.
Police said the train came into the station as the girl was trying to climb back on to the platform.
She was taken to Elmhurst Hospital, where she died, police said.
Commuter Stephen Topete told ABC New York that people were crying on the platform after the incident.
After the accident, New York City Transit released a statement urging customers to alert subway staff if they drop something on to the tracks rather than trying to recover it themselves.