In 1898 Mrs. Lothrop entered the Associated Charities of Boston as worker in training; 1900-3, district secretary in the Associated Charities; 1902, summer course in the New York School of Philanthropy; 1903-13, general secretary of the Associated Charities of Boston; 1904-20, lecturer and special assistant in the Boston School of Social Work; 1906, relief work after the San Francisco fire; 1908, relief work after the Chelsea fire; 1910-11, aided in the formation of the National Association of Societies for Organizing Charity; 1913, resigned as general secretary of the Boston society to be married, and was made one of its directors; 1914, relief work after the Salem fire; 1914-20, chairman of the American Association for Organizing Charity, later changed to “Organizing Family Social Work”; 1917, secretary of the Plan and Scope Committee of the Boston Metropolitan Chapter, American Red Cross; 1917, Red Cross relief work after the Halifax explosion; 1917-19, Director of Civilian Relief in the New England Division of the American Red Cross.