In Reed Morano’s new film, I Think We’re Alone Now, opening Sept. 14, a misanthrope (Peter Dinklage) believes he’s the sole survivor of an apparent apocalypse until he runs into a mysterious young woman (Elle Fanning). As one of the few female directors who also serves as her own cinematographer, Ms. Morano may feel almost as alone. But that didn’t stop her from taking on that demanding dual role with her first movie either, the 2015 grieving-parents drama Meadowland.