Petra - Allendian Post-Apocalypse, #1

She's their friend, their protector, their keeper; and their assassin. On a remote planet with two moons lies a dome. Where once its modern city homed thirty thousand Allendians, it now sits quiet, empty but for the one that stalks its streets, hunting for the last of the ill, removing them from its surface so that the re-emergence can happen. Ten-year-old orphan Sidney lives in these empty streets, scratching the grounds for scraps and hiding from the one that will kill her.
She means to find her way to the lands her mother talked about, the lands where she can get healthy again, and she knows she will succeed. Until the killer catches up to her. For fans of Westworld, Humans, Ex Machina, etc.