Clotilde Deflandre passed her baccalauréat in 1899 and went on to study at the Paris Faculty of Science.
After obtaining a doctorate in science in 1903, she began a career in secondary education while continuing her research. Appointed science teacher at the Roubaix girls’ college, she took advantage of her geographical proximity to the Lille Combined Faculty of Medicine and Pharmacy, and the links between her mentor Augustin Gilbert and Lille professor Hyppolyte Surmont, to undertake a doctorate in medicine, which she defended in 1910.
She seemed to pursue her teaching career until she married Léon Dufour, a Fécamp doctor and founder of La Goutte de lait, in 1921. She then practiced medicine with her husband. Some time after his death in 1928, she undertook new scientific research and published articles in 1931-1932 with Dr Gaston Roussel, founder of Usines Chimiques des Laboratoires Français (UCLAF).