The Defiant Princess (translated)

Humble office worker Seraphina Gu finds herself transmigrated into the body of the eldest daughter of the Chancellor's Estate in the Daesung Kingdom. The original daughter, a meek pushover unloved by her family, was forced to marry the notoriously cruel Prince Jing, Jasper Xiao, in her sister's place. However, she is murdered on her wedding night in a plot orchestrated by her sister, Angelica Gu, and her beloved Crown Prince. Reborn with a new life, Seraphina uses her modern-day wisdom to protect herself and begins her ascent. She cleanses her family of its corrupt members and retaliates against the villainous Crown Prince. During this time, Seraphina discovers that the Gu poison afflicting Jasper Xiao was the Crown Prince's doing. To cure the poison, Seraphina repeatedly confronts the Crown Prince, joining forces with Jasper Xiao to expose his true nature. They ultimately bring down the Crown Prince, and in the process, find true love with each other. (translated)