Fielding insisted upon retaining the everyday use of the Mohegan language during an era when most New England Native peoples were becoming increasingly fluent in English. Her maternal grandmother Martha Uncas spoke it with family members, and other Mohegan people continued to speak and understand some of the language, but by 1900, few were as fluent as Fidelia and her sister. As an adult, Fielding kept four diaries in the language, which later became vital sources for reconstructing the syntax of Mohegan Pequot and related Algonquian languages.