Blood Of A Traitor by Sandra Barret

Kay has no official family, no official name, just a gene line designation and a crappy future thanks to the Nassien Research Division. As the sole Terran genetic experiment in a Novan Marine outfit, her life is a never-ending conflict. When her Novan ship comes under attack from unknown assailants, she becomes a part of the dreaded Black March and an aide to the enigmatic Lieutenant Colonel Nassien. As the only world she's ever known crumbles around her she no longer knows who to trust