Vengeance of the Pirate Queen by Tricia Levenseller

You can’t be afraid of the dark when you’re the monster lurking in the shadows.Eighteen-year-old Sorinda is a deadly assassin with a reputation to match. But her latest assignment is like no other. The pirate queen, Alosa, has tasked her with captaining a handpicked crew on a dangerous rescue mission, and her sailing master is none other than the infuriating Kearan. But as they navigate through treacherous waters, they accidentally awaken the King of the Undersea, who summons an army of undead soldiers from the depths. With Kearan by her side, Sorinda must fight tooth and nail to survive. Will Sorinda and her crew manage to save the world, or will she face a fate worse than death – becoming an undead queen controlled by the King himself?