She Drives Him Dark

Ruan Tang accidentally falls into a book world, arriving just as the original heroine marries the Shen family to bring luck to a deceased husband, leaving only his young brother, Shen Xiuyuan. To return to reality, a system suddenly appears and assigns her a mission: she must strictly follow the main plotline, personally drive Shen Xiuyuan toward his dark transformation, and help the story progress along its original path. Only then can she find a way back to her original world.