Okay... first off, her backstory doesn't really work, since when she was four the Galactic Empire was in full swing. There were only two actual Sith, and even now it's more Dark Jedi trying to be Sith than anything. Then... her personality, well... She doesn't have to be a totally evil person in every way, but the Dark Side is a Dark Side. Letting hate and anger reign over you is what it's all about.