She was the fastest girl in the United States. Then she joined Nike.
From the New York Times's opinion section:
At 17, Mary Cain was already a record-breaking phenom: the fastest girl in a generation, and the youngest American track and field athlete to make a World Championships team. In 2013, she was signed by the best track team in the world, Nike’s Oregon Project, run by its star coach Alberto Salazar. Then everything collapsed.