Namjajuingongi Naege Cheonghonhaetda

Ciel wakes up in a novel as the villainess who torments her adopted sister and the female lead, Clara, until she’s executed for her misdeeds. Determined to avoid this fate, she becomes the sweetest sister, doing anything for Clara’s happiness. But to her surprise, her efforts end up altering the plot, eventually leading Prince Alex, the male lead, to propose to her instead of Clara! Will accepting his proposal bring Ciel the happy ending she desires? Or will it only bring her greater challenges?

(Source: Tapas)