Mia Eriksson, 17, suffered a fatal accident while competing in a three-day event at Galway Downs in November 2006. Eriksson's mount, Koryography, fell at fence 19, and crushed his rider.
A full paramedic team attended within moments of the fall, organisers said. Eriksson was taken to the Rancho Springs Hospital, Temecula where she died.
The New York Times reports that her parents filed a lawsuit in a California court on May 6 against the US Equestrian Federation and the US Eventing Association. The suit alleges that the course was made more dangerous "in order to make the competition more thrilling to spectators", and also alleges that equipment used on the course was defective.
"Mia for the USEA is a statistic, but she is really so much more than that," her mother, Karan Eriksson, told the New York Times.
"I stepped forward to file a lawsuit trying to voice in a way all of the concerns we're feeling at the level of eventing to press for change."
Many deaths and serious injuries to both horses and riders have occurred in eventing in the past few years. The US Equestrian Federation is running an eventing safety summit in Lexington, Kentucky, on June 7-8, and the sport's world governing body, the FEI, is undertaking a study into the accidents and injuries sustained by riders.