Sarangeun Eobsneun Geotcheoreom

Si-Yeon had the rug pulled out from under her when she realized that everything in her life was a lie-- her parents are not her real parents, her fiancé not really her fiancé, and her cousin Eun-Hye is actually the birth daughter of this household. Si-Yeon is resigned to her misfortunes until Eun-Hye reveals to Si-Yeon that all of this was planned and orchestrated. Swallowing her tears of anguish, Si-Yeon makes a fateful wish that brings her 10 years into the past where she may be able to change everything... or can she?

(Source: WEBTOONS, edited)