However, in Athens she was eliminated in the first round of the women's 49kg competition by losing 5–9 to Yaowapa Boorapolchai of Thailand.
Diaz defeated Yaowapa Boorapolchai of Thailand in the quarter-finals and Euda Carias of Guatemala in the semifinals but was defeated in the finals by Chen Shih-hsin of Taiwan to win the silver medal.
She defeated Ivett Gonda of Canada and Gladys Alicia Mora Romero of Colombia in the repechage tournament to win the bronze and become the first Thai Olympic medalist outside of boxing and weightlifting.