The name of the new Guren references a Hindu god and some ancient Indian guy. Kallen is the only person on the show who pilots the Guren. Kallen isn't defecting unless a certain scientist who shares Indian heritage also defects. The likelihood of that happening under any circumstance is really, really low.
Plus, why would Kallen ever, ever, think about joining up with someone who plans to drug her with the highly addictive substance that ruined her mother's life?
Further, I doubt Sunrise would spend an entire season building up romantic tension between Kallen and Lelouch to throw it away on a whim by having Kallen cease to believe in per personal Jesus when the going gets tough.
Kallen isn't defecting. Had you suggested that she would before last week's episode, I would have placed stock in the possibility, but I just cannot see her ever siding with someone who she has been against the entire show, who is currently trying to drug her for information.