The Crown of Blood and Fire: Assassin's Revenge, Book 1

Lethal assassin. Secret princess. Good with knives.
Larina Dracomeer has waited fourteen years to kill King Elrin, the usurper who murdered her royal family to steal the throne of Oramis. Whisked to safety and trained in the deadly arts, Larina has dedicated her entire life to become a cold-blooded killer, capable of avenging her loved ones.
When a job opportunity arises to be the personal bodyguard of Elrin's son, Prince Dezrick, Larina jumps at the chance to secure her place in the false ki...