She did not take part as an athlete, but rather won as the trainer of the horse.
In 396 BC, the wealthy Spartan princess and horse trainer Cynisca became the first woman to win an Olympic event. She did not take part as an athlete, but rather won as the trainer of the horse. The trainer, or owner, of the horses was deemed to be the winner of a chariot race, rather than those controlling the chariot (who could only be male).