"Snow White and Rose Red" by Jessie Willcox Smith. Frozen was widely heralded for its focus on a sister relationship instead of a romantic one—the first Disney fairy tale retelling that was about a bond between sisters. But the movie was (extremely loosely) based on The Snow Queen—a fairy tale that doesn’t even have a sister in it. My upcoming middle grade book, Thornwood, is told from the point of view of Sleeping Beauty’s little sister, and is going to kick off a series of retellings, called Sisters Ever After, about “the sisters the fairy tales left out.” I had a lot of fun weaving the complexities of a sister relationship into a story that was originally about an only child. But at some point I started to wonder: why does a fairy tale about sisters seem like such a novel concept? After all, most fairy tales didn’t originate at a time when only children were the norm. Yet a search through popular fairy tales reveals a smattering of sister-brother combinations, and a couple of jealous, conniving sisters, but not many sisters who work together.