I Can't Stop (2007)

Hong Yun Shi was a pure and innocent girl who remained cheerful despite growing up in poverty. Her unfortunate circumstances drives her to marry the rich Byung Joo, but she is soon betrayed by her husband and her mother-in-law. When she discovers that her mother-in-law also had a hand in her mother’s mysterious disappearance, Yun Shi finds herself slowly losing all semblance of her original purehearted self and turning into someone obsessed with revenge. Soo Ri, who loves Yun Shi deeply, is helpless to do anything but watch over her with warmth and love.