[Mal]
It's a little more complicated than that. Niki has something called "Dissociative Identity Disorder". Basically it's like a split personality. The one you know and have seen is Niki. Jessica has been hidden for a long time - years, really - but when Niki is threatened, or feels unsure of herself, Jessica comes out to protect her. Or to 'fix' things how she thinks they should be.
The problem is, Jessica is a maniac, who seems to enjoy breaking people in half. Literally. Hence, why we had to give her the sedatives.