A two-time National Champion before she was 18, Harrison became the third U.S. player ever to win the Junior World Championships in 2008 after going undefeated to win the 78kg title in Bangkok. Harrison, who moved up from 63kg to 78kg in 2008, won the U.S. Olympic Team Trials for Judo that year, but was unable to compete at the Games as Team USA had not qualified the division. In 2009, Harrison became the second U.S. athlete ever to compete in two Junior World finals where she won a silver medal. Harrison made her mark on the senior international level in 2010 when she became the first U.S. woman to win a World Championship in 26 years, going undefeated in five matches to win the gold.