Boole's husband was active in prohibition and temperance activities, in which she joined him. Boole joined the Women's Christian Temperance Union (WCTU) in 1883. She showed great skill as an organizer of new unions, and became vice-president of the New York state union in 1891. After the death of Boole's husband, she was able to support her family through an inheritance from her father and income from her speaking engagements and temperance activities. In 1898, she became President of the New York WCTU. She held this position until 1925, with the exception of a six-year period when she was corresponding secretary of the Woman's Board of Home Missions of the Presbyterian Church (1903-1909). One of her key activities was in shifting WCTU work away from its emphasis on collecting petitions, and towards direct lobbying of legislators.