The poison daughter By Sheila Masterson

The Poison Daughter is a standalone romantasy about Harlow Carrenwell, the youngest daughter of a magical founding family whose kiss is deadly. She has used her poisonous gift as an assassin for her family while secretly hunting abusive men as a vigilante.

Everything changes when Harlow kisses her latest target and he survives. The man is Henry Havenwood, her new betrothed and a member of a rival family. Instead of exposing her secret, Henry takes Harlow to his mountain stronghold, forcing the pair to work together to uncover what his family is planning while navigating a dangerous enemies-to-lovers attraction.