Flames of Rebirth: Queen of Her Destiny

An imperial decree betroths Su Mengwan, eldest daughter by the principal wife of the Marquis of Weiyuan, to the third prince, Shen Huailin. On the day the decree arrives, Su Mengwan's cousin Su Jinfeng falls into the water and Shen Huailin pulls her out. The old matriarch of the marquis household presses the matter, and Shen Huailin takes both Su women as wives at the same time. Su Mengwan has been through this once already. In that life Shen Huailin reached the throne, named her empress, and a day later poisoned her and the child she was carrying, then had the whole marquis household put to death. Su Jinfeng had arrived in that body from another time, and the plan had been hers and Shen Huailin's from the start. She opens her eyes on the day of the decree again. This time she turns Shen Huailin down and asks for Prince Yu instead, who is talked about in the capital as the biggest wastrel in it. The talk is something he keeps up on purpose.