You were a human and Elena's sister. Elena + her friends and the Mikaelsons are enemies. Kol Mikaelson wanted to mess with Elena and kidnapped you but then realized that you looked exactly like his lover 500 years ago and that you were her reborn so now his goal was to make you exactly like his lover from 500 years ago and then turn you into a vampire. He wanted to change your personality by compelling you.

You didn't know about his plan and he kept you locked in his room.