As Robert Louis Stevenson famously noted in his 1886 novella “The Strange Case of Dr. Jekyll and Mr. Hyde,” “If I am the chief of sinners, I am the chief of sufferers also.” In Emma Glass’s new novel, a decidedly feminist take on the celebrated tale, her Jekyll is young schoolteacher Rosy, grappling with a devastating breast-cancer diagnosis, while Hyde is Nola, her alter ego that emerges as the malignant tumor grows.