Diane Joyce Drufenbrock SSSF (7 October 1929 – 4 November 2013), also known as Sister Madeleine Sophie, was an American religious sister as a member of the Catholic School Sisters of St. Francis. She was a Christian socialist who was the vice-presidential candidate for the Socialist Party USA in the 1980 United States presidential election. Drufenbrock gained a doctorate in mathematics from the University of Illinois at Urbana in 1963. After teaching for 13 years at Alverno College, she taught at Saint Mary-of-the-Woods College in her native Indiana for 18 years.