Scarlett O’Hara scandalized polite society a few times in Gone With The Wind. She opened her own lumber mill and later staffed it with convicts from a local prison. Money was scarce in war-torn Atlanta, but proper ladies had proper jobs, like painting china at home and selling it. Scarlett pooh-poohed that.
Magazines were very popular entertainment in the days before television. Illustrations in were often printed on smooth, heavy paper, called plates. (Does anyone remember books with Plate 1 and Plate 2, instead of Fig. 1 and Fig. 2?)
Fashion plates were illustrations showing the latest styles, and often showed well-dressed women in (ladylike) action.
This was printed as a black outline and dropped off at a woman’s house, and she added the color with paintbrushes. This was a way women could work at home, because it was not considered acceptable for a woman to work in an office with men.
Later, the term “fashion plate” came to mean a woman who wore stylish clothes.