Hennin was born in either 1963 or 1964,[1] and comes from Windsor, Ontario.[2] She is a graduate of William Hands Secondary School and of St. Clair College, where she qualified to be a medical secretary.[3][4] Hennin had cerebral palsy that has caused her legs to be paralyzed.[3][4] She competed in the C4 category in track and field events,[5] and was trained by coach Doug Wilton.[4] Hennin commenced competitive swimming when she was 14 years old,[3] and she would be encouraged by her parents to train despite their initial apprehension she would be injured doing swimming.[3]
She won five gold medals in the D cerebral palsy division at the 1980 Regional Games for the Physically Disabled in Brantford.[6] Hennin claimed four gold medals in the 50-metre freestyle swimming, the 100-metre sprint, the pentathlon and shot put with a new United States record of 12.5 ft (3.8 m) throw and won two silver medals at the Michigan International Games for Cerebral Palsy Athletes at Ypsilanti, Michigan.[7] At the Ontario Games for the Physically Disabled at Sault Ste. Marie, Ontario, she took five gold medals in the 25, 50, 100-metre freestyle swimming and the 60-metre wheelchair dash and the discus throw events and recorded four new Ontario records.[1]
Hennin took four gold medals in the 50 and 100-metre freestyle swimming, the 100-metre wheelchair and the club throw competitions and three silver medals in the 4 x 25-metre swimming relay, the discus throw and the 200-metre sprint at the 1981 World Invitational Cerebral Palsy Games at Nottingham, England.[2] At the 1981 United States National Cerebral Palsy Championships in Kingston, Rhode Island, Hennin set three new American records in the 25-metre and 50-metre freestyle swimming competitions and in the discus throw.[8] She was part of the Windsor soccer team that won the gold medal in the cerebral palsy division with victories over Toronto and Michigan Tri-City at the 1982 Windsor Classic Games for the Physically Disabled.[9]
As a member of the Windsor Bulldogs at the 1982 Regional Games for Disabled Athletes, Hennin won the gold medal in each of the 25, 50, 100-metre freestyle swimming, the discus throw and the 200-metre dash competitions.[10] She earned 1982 Disabled Athlete of the Year honors for both Ontario and Windsor.[3] She earned five more medals in the 25, 50 and 100-metre freestyle swimming as well as the 200 and 400-metre sprints at the 1983 Ontario Games for the Physically Disabled in Brampton.[11] Hennin went on to claim a further four gold medals in the 50 and 100-metre freestyle swimming, the 800-metre and the discus throw events at that year's United States National Championships and earned selection to the 1984 Summer Paralympic Games training camp.[12]
In May 1984, she was accepted as a member of the Canadian Paralympic team at the 1984 Summer Paralympics held in New York City the following month after winning four gold medals at the 50-metre freestyle, 50-metre backstroke, discus and the 4 x 50-metre freestyle competitions at the Michigan Regional Cerebral Palsy Games.[13] Hennin won the silver medal in each of the women's 50-metre and 200-metre freestyle C4 events and a single bronze medal in the women's 100 freestyle C4 events.[5][14] She also competed in the women's discus throw C4 and women's 100-metre backstroke C4 competitions where she finished fifth and fourth respectively.[5]