Day 6: 6:00 AM - 7:00 AM - S6-E1
Jack Bauer: Do you understand the difference between dying for something and dying for nothing? The only reason I fought so hard to stay alive in China was because I didn't want to die for nothing. Today, I can die for something.
Day 6: 10:00 AM - 11:00 AM - S6-E5
Graem Bauer: Actually, you're hurting me right now.
Jack Bauer: Trust me. I'm not.
Day 6: 9:00 AM - 10:00 AM - S6-E4
Bill Buchanan: We have to do better than we're doing, and we have to do it faster!
Day 6: 8:00 AM - 9:00 AM - S6-E3
Hamri Al-Assad: I do not work with my enemies.
Jack Bauer: You're working with one now.
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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