Sargent was born in Pasadena, California. Her father was a surveyor who helped rebuild the Tioga Road in Yosemite National Park, starting in 1936. She had the good fortune of spending her childhood as a self-described “tomboy” in Yosemite. A rare crippling disease, dystonia musculorum deformans, kept her to a wheelchair from age 14, but that didn’t stop her.
After writing Wawona’s Yesterdays, she went on to write several other Yosemite History books, focusing on stories about people—making them come alive. Her most authoritative book is Galen Clark: Yosemite Guardian. Shirley self-published most of her books, with printer and historian Hank Johnson, under the name Flying Spur Press, and later under her own imprint Ponderosa Press. Other popular books of hers include Pioneers in Petticoats, John Muir in Yosemite National Park, Yosemite & Its Innkeepers, and Yosemite Chapel 1879-1989.
In 1961 she bought and built on Theodore Solomons' homesite in Foresta, California, which had only a fireplace surviving from a 1936 fire. She called her home Flying Spur, but it burned in the 1990 Yosemite A-Rock Fire, which also destroyed her historical papers. She rebuilt her home, but before her death she had to move to her parents’ old home in Mariposa, California due to her illness. She died at her home there.