After the Crown: The Indranan War, Book 2 by K. B. Wagers
Former gunrunner-turned-Empress Hail Bristol was dragged back to her home planet to fill her rightful position in the palace. With her sisters and parents murdered, the Indranan empire is on the brink of war. Hail must quickly make alliances with nearby worlds if she has any hope of surviving her rule. When peace talks turn violent and Hail realizes she's been betrayed, she must rely on her old gunrunning ways to get out of trouble. With help from an old boss and some surprising new allies, she must risk everything to save her world.