Shadow of Dawn by Cynthia Patrice

Even wizards need to be careful who they murder.
Seventeen-year-old Camilla lives a pleasant, protected life in a land full of magic and wonder. All that changes when the young noblewoman’s family is butchered in front of her.
With enemies all around her and death a single misstep away, she now lives for vengeance. How can she possibly achieve that goal when her enemies include both wizards and kings? By joining the Guild of the Whispering Blade, training to be an assassin, and finding allies in a skilled elf, a handsome prince, and his equally handsome cousin.