In 1915 Whittemore organized state branches of the Congressional Union in California, Michigan, and Ohio. Her sister-in-law, Marjorie Miller Whittemore, became head of the Michigan branch of the subsequent National Woman's Party.[2]
Through the NWP Whittemore was involved in advocating for federal suffrage in the western states of Washington,[3] Oregon,[4] and Idaho. In 1917 she was arrested and spent three days in jail along with several other suffragists for picketing the Wilson administration in front of the White House.[5] In 1918, she was head of the Idaho election campaign where she was unsuccessful in the campaign to persuade Idaho Senator William Borah to support the vote for the suffrage amendment.[6]
In 1922, after women had won the right to vote, Whittemore continued her activism, specifically she and Mabel Vernon drove from Indiana to California, supporting women candidates running in the 1924 elections. In 1925, Whittemore became one of five vice-presidents of the National Woman's Party.[2]