Born in Michigan, Custer was one of four children. She is known for being an outspoken advocate for her husband, General George Armstrong Custer, through popular books and lectures. She wrote Boots and Saddles, Tenting on the Plains, and Follow the Gidon which are all aimed at glorifying her husband after President Grant and other senior officers blamed General Custer for the Indian massacre of his battalion.
After his death she was hired by Candace Wheeler and Mary Mapes Dodge to be their personal secretary. She later built her own home in Onteora Park, "The Flags."