De Mars was born on the Scott Air Force Base in Illinois. She grew up in the small community of Alton, Illinois and began her judo career at the age of 12 at a local YMCA.

De Mars won her division at the USJA Junior Nationals at the age of 16 – her first major competition. The same year, she entered college at Washington University as a business major. At the age of 18, as a college junior, De Mars was an exchange student at Waseda University in Tokyo, Japan. While there, she trained under Sensei Osawa.

She graduated from college with a degree in business in 1978. She also won the US Senior Nationals, US Collegiate Nationals and the US Open. In the absence of women’s judo world championships, she quit competitive judo and studied for an MBA at the University of Minnesota.

De Mars earned her MBA in 1980. She missed the first women’s world championships while in grad school, but in 1981 won bronze in the British Open and Tournoi d’Orleans. In 1982, she was ranked #1 in the USJI rankings and won the US Open. However, she did not contest the second women’s world championships due to the birth of her daughter María.

De Mars enjoyed more success in 1983, including the Pan American Games and US Senior Nationals, and in 1984, winning the Austrian Open, Canada Cup (now known as the “Rendezvous”), and the US Senior Nationals. She came out of retirement to win the 1984 World Judo Championships, becoming the first person representing the United States to win a World Judo Championships (her name at the time was Ann-Maria Burns).

She says on her web page “One world championship, a million dollars in contracts, four degrees, four children – and I still don’t know what I want to be when I grow up.”