Mary Miller continued to be a leader in the community, especially in January 1900, when the town's business district burned. She founded the Farmers’ & Miners’ State Bank with S.T. Hooper, C.C. Brown and G.C. Beaman in June 1892, which closed in August 1894. Mary Miller then formed the Lafayette Bank in 1900. She was elected president of the bank, and according to a Denver Post article reprinted in the Lafayette News and dated December 13, 1902, was "the only woman in the United States known to be president of a bank." The bank closed in 1914 because of roughly $90,000 in bad loans to the striking United Mine Workers. Mary Miller remained devoted to the temperance movement and eventually ran on the 1913 Prohibition Party ticket for the U.S. Senate seat won by Gov. John F. Shafroth. She also ran for the state treasurer seat on the Prohibition Party ticket. Miller died in 1921 at her daughter-in-law's home at 501 E. Cleveland Street.
