In the Vampire Diaries, S02, How come Katherine manages to get her hands on the exact same clothes as Elena and act as her? This happens multiple times throughout the season. Stefan asks this question to Katherine in one of the scenes but she doesn't replies.
That is because Katherine was a Doppelgänger who can take on the look and traits of Elena. Including her cloths and behavior.
It's an evil force that brings evil or misfortune.