Vivian Maier and the Problem of Difficult Women

“Why would a nanny be taking all these pictures?” Maloof asks in “Finding Vivian Maier.” His puzzlement reflects the central anxiety of the film, and of the Maier legend in general. Why would a photographer with the fierce dedication, creative vision, and formal skill of a Robert Frank, a Diane Arbus, or a Garry Winogrand withhold her work from the world and choose instead to spend her life raising other people’s children?