Born in Milwaukee, Flanders earned a B.A. in Botany from Smith College in 1914 and a B.S.L.A. from the University of Illinois in 1918. In 1920, she went to work for Vitale, Brinckerhoff and Geiffert in New York City. After two years, she opened her own practice, employing Helen Swift Jones and, later, Helen Elise Bullard. Flanders closed the New York office in 1942 and opened an office in Milwaukee the following year.
Flanders worked primarily in the Eastern and Midwestern United States. Her work included estates, subdivisions, and model gardens, both formal and informal, using native trees and shrubs. Her commissions included the Phipps Estate, the Morven Farm Gardens, and the McCann Estate French Gardens, which received the Architectural League of New York’s Medal of Honor in Landscape Architecture in 1932.
She lectured on a variety of landscape topics, promoting simple, livable, and economical garden design. Flanders wrote for several magazines, including House and Garden and House Beautiful, and she worked as Good Housekeeping’s consultant garden editor from 1933 to 1934, publishing a four-part series on suburban garden design. She was recognized in Home & Garden’s Hall of Fame in 1930 and elected as Fellow of the American Society of landscape Architects in 1942. Flanders continued to design and publish until her death.