The contact owns a 2019 Ford F-250. The contact stated that while driving approximately 15 MPH, the rear sliding glass window suddenly fell from the window frame and made contact with the granddaughter who was in a booster seat positioned in the middle of the rear seat. During the incident, the granddaughter sustained a head contusion that did not require medical attention. The cause of the failure was not determined. The vehicle was not yet repaired. The local dealer and manufacturer were notified of the failure. The failure mileage was 55,000.