The Black Guard: Book I: Least Favorite Child (Black Guard series 1)

As the least favored child, it was no surprise when Rivka's father selects her, at age six, to comply with the country's conscript law. Sent away to the military to be raised and trained, she struggles to keep from falling into an abyss of despair. Only when she adopts a new friend's dream of becoming a member of the elite Black Guard does she find a new reason to live.
Few make it into the Black Guard, but Rivka is determined. Yet when she makes it and is sent on her first mission, to protect a ruling family during a revolution, she discovers to her dismay that the Black Guard may not be as perfect as she had believed. Thus Rivka begins a journey that will change her and the Black Guard forever.