Factual error: When Janet enters the operating theatre, the surgeons put some x-rays on the light box. The x-rays are from a barium enema, which would have no relevance to Janet's injuries.
Factual error: Janet would have been in surgery for several hours, instead of just 40 minutes or so.
Answer: According to Jack in season 5, Nina was "deep cover" before the pair ever met, so it's safe to assume she was recruited before she joined CTU. As for what her primary mission was, who knows? Perhaps it was to gather sensitive intel and pass it on to her superiors. Given that she worked for an intelligence agency, it's not a stretch. Or perhaps we may find out in season seven.
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