Ansie was born in Amsterdam on 6 April 1955, then emigrated to South Africa and settled in the Orange Free State, where she matriculated at Sasolburg High School. Her coach was the Australian Jim Spring.
At the 1970 South African Championships held at the Hillcrest Pool in Pretoria, Ansie finished third in the 800m freestyle, behind fellow Freestater Pietie Horn and Jean Burden of Rhodesia.
At the 1971 Championships at Newlands in Cape Town, Ansie beat Pietie in the 400m freestyle and came second to her in the 800m event. She also placed second in the 200m freestyle behind Katink Germishuis. Pietie also won the 200 fly and 400IM events. For these achievements, Ansie was awarded Springbok colours to compete against Rhodesia.
At Newton Park Pool in Port Elizabeth for the 1972 SA Championships, Ansie again took the 400m title and placed second in the 200 and third in the 800m freestyle events. Ansie beat the sensational Sue Dickie in the 400m event, after Sue had set a new SA record for the event in the heats.
The South African Championships of 1973 were held at the Borrow Street Baths in Bulawayo, where Ansie finished second in the 200 and third in the 100m and 400m freestyle events. Later that season the South African Games held in Pretoria featured a number of foreign swimmers - Olympic medallists and world record holders, including David Wilkie (GB), Klaus Steinbach (Germany), and Ann Simmons (USA). Ansie finished third behind Sue Dickie and Ann Simmons in the 200m freestyle. She later placed 4th in the 400m event, behind Dickie, Simmons and Christine Meal of Rhodesia. In the 100m, she was second to Esme Oosthuisen, beating Françoise Monod of Switzerland.
In 1974, Ansie only managed a 6th place in the 100m freestyle, and in 1975 she did not make the final.
Ansie disappeared from the swimming sections of the newspapers after that, and re-appeared in later years when she settled in the Cape, where she was active in the Rotary Club of Stanford.
1968 - Olympic SC coach Jim Spring and his wife Rona, with Ansie Reitsma and Louie de Goede, after their successful tour to Darmstadt, Germany.