Villainess reborn manwha

The FL is read haired is from a clan with super strong people that have fighting danse. All the clan is exterminated for some reason except for her and a blond emperor take her as her slave. The step brother of the emperor was revolting and plan to kill the emperor to take the power. So then during a party the FL kill the blond and the black haired step brother become the king and her become his right hand. The black haired die too (I think she kill him) and then SHE take the head of the empire. She become the most powerful empress I think. She dies.
Years after she's reborn into another family with the same appearance and a sister. She's the smartest of the academy and one time her teacher ask a question about her past self and she answers because the empress (so her) loved the black haired guy and everyone laugh.
Her sister has to marry a man but she choose to marry him herself.
Please help me I'm desperate