Sister Diane Joyce Drufenbrock, S.S.S.F., (born 7 October 1929 or 1930 in Evansville, Indiana), also known as Sister Madeleine Sophie, is a member of the School Sisters of St. Francis and a Christian socialist who was the Vice-Presidential candidate for the Socialist Party USA in the United States presidential election, 1980.
In 1948, Drufenbrock moved to Milwaukee to enter the Franciscan Sisters. A mathematics graduate of Alverno College in 1953 and of Marquette University, she has taught mathematics at Alverno College, at the University of Wisconsin–Parkside, and elsewhere around Milwaukee, Wisconsin, including at the then-new St. Joseph High School (Kenosha) when it opened its doors in September 1957.
Her interest in social issues led her to join the Socialist Party USA in 1976. She ran as their Vice-Presidential candidate in the 1980 United States presidential election, and has served as that party's National Treasurer. That campaign resulted in the Party's recognition by the Federal Elections Commission as a national political party.