Forbes, born Kathryn Anderson, was the granddaughter of Norwegian immigrants. She was a writer best known for Mama's Bank Account, a fictionalized memoir about a Norwegian family in 1920s San Francisco. The book focused on the warmhearted family and its struggles and dreams. The book inspired first a play, then a movie, and finally a TV series, all called I Remember Mama.

Forbes also published novel called Transfer Point, about a daughter of divorced parents. This was considered to have been based on Forbes' own childhood.