Ly defeated Apasara Koson of Thailand 30-27 in the final.
Earlier, Ly beat Gabriela Kuzawinska of the hosts in the semi-finals and Atenea Flores from Spain in the quarter-finals with the same score of 30-7.
Her teammate Dao Le Thu Trang and Dao Thi Nhu Quynh were ousted in the group round, also in muay.
Vo Van Dai lost in the quarter-finals of the men’s 63.5kg.