At the age of 14 years and 4 months, Edmondson was an Australian Paralympic competitor. She was the youngest competitor at the 1964 Summer Paralympics in Tokyo among athletes from all nations. She was the youngest Paralympic gold medallist for Australia for 48 years, until Maddison Elliott won a bronze medal at the 2012 London Paralympics. She won three gold medals in the 1964 Summer Paralympics in the following events: the women's class 5 50-metre breaststroke with a world record time of 1.04.6; women's class 5 50-metre backstroke with a world record time of 0.50.8; women's class 5 complete 50-metre freestyle with a world record time of 0.39.7. At the conclusion of the 1964 Games, Edmondson's parents acknowledged that swimming had greatly helped their daughter, but felt that she needed to quit the sport and concentrate on her education because swimming would not provide her with standing in life. After the 1964 games, Edmondson returned home and prepared for school exams.