Hounds of Gaia. The Marrower Saga, #1

Foxhound doesn't care about the gaps in her memory. Being a Contractor, a kind of spacefaring mercenary, keeps her occupied enough. Rather than dwelling, she rockets around the farthest reaches of the solar system, earning a steady paycheck hunting down ne'er-do-wells and enjoying a semblance of freedom most folks in the outer colonies can't dream of. So when she receives an urgent prisoner transfer request from a cult starship, she accepts the gig.
She figures that transporting a bone marrow-eating serial killer from the cult's colony back to Earth is just another well-paying job that'll keep her mind off things. Upon discovering that the suspect in custody is an orphan girl-one that could pass for her much younger doppelgänger-she decides it's time to get some answers. Before she can piece together who the girl is and how their lives intertwine, a group of violent prisoners aboard Foxhound's starship breaks free.
As the once-peaceful cultists take up arms in response, the Contractor teams up with her mechanized AI assistant and two of the cult's wayward members to stop the barbaric escapees and elude the grasp of the cult's radicalized leader. And when that's done, she can focus on figuring out the secret behind the mysterious, potentially dangerous girl-but will she even want to know the truth?