The Sin Eater's daughter

For four years sixteen-year-old Twylla has lived in the castle of Lormere, the goddess-embodied, whose touch can poison and kill, and hence the Queen's executioner--but when Prince Merek, her betrothed, who is immune to her touch returns to the kingdom she finds herself caught up in palace intrigues, unsure if she can trust him or the bodyguard who claims to love her.