I believe Bell probably is perfect, or as near to it as any other young actor on TV that I can think of.
Having also seen her play a combination of scary, manipulative and sociopathic as shit while also being pretty close to dumb as a sack of hammers, at least in terms of knowing what she was up against, on DEADWOOD, I totally agree with you there. She's got SMG's technical chops, but she can project a whole lot warmer (or colder) when she wants to. Caroline D. from WONDERFALLS could give her a run though, I think.