Return of the Heiress (2013)

Spoiler: these 2 dramas have a similar ending both ends but the girl having two choices but the ending never said about what kind of choices they made.

Cinderella's sister is a K drama
Return of the heiress is a C drama
Both are sad stories
I liked them both, though I did enjoy watching return of the heiress more
If you liked return of the heiress then you should try watching Cinderella's sister

both involve a main female lead who sets out for revenge against the people who have wronged her. Both have intelligent and awesome main female leads who know exactly how to step on the throats of the ones who wronged them. They also both involve a rich family that have something to do with the main female lead and is about how the main girl fights back to reclaim what is rightfully hers.

Both about family betrayal
Both have a strong FM
Both seek revenge
Unknown woman is a K Drama while Return of the Heiress is a C Drama