Sinclair was the first female inductee into the National Lacrosse Hall of Fame. She taught at Bryn Mawr School in Baltimore from 1925-51. Shortly before her death in 1978, she had the pleasure of knowing that an athletic field at the school had been named in her honor.
A graduate of St. Leonard's School in Scotland, where woman's lacrosse originated, Miss Sinclair introduced the sport at Bryn Mawr in 1926. Although the parents at Bryn Mawr required convincing that lacrosse was safe for their daughters to play, she succeeded in starting a team that continues to play today, the oldest team in the country. By 1928, Sinclair had taught lacrosse to high school teams and and clubs around Baltimore.
The game soon spread to Philadelphia, New York and Boston, and in 1931, the United States Women's Lacrosse Association was formed. Sinclair was a stickler for perfection, using lacrosse to teach hard work, discipline, patience, steadfastness of purpose, achievement and motivation.