She tried to get on Michael's raft because she was afraid that if the Losties were rescued, she would be identified as a wanted fugitive. She reasoned that she'd have a better chance of escaping rescue/capture on the raft. Besides, S1 Kate was "born to run." Her natural instinct ws to flee when things would heat up. As far as her being used by Smokey, it's possible, but unsubstantiated at this time.