Revealing mistake: Throughout season 2 on several occasions it's clear that John Terry (Bob Warner) is wearing a fake mustache and a fake beard.
Factual error: Invoking the 25th amendment cannot be done by vote. The members have to send in their written declaration that the President is unable to discharge the powers and duties of his office, the Vice President shall then immediately assume the powers and duties of the office as Acting President.
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.
Cubs Fan ★