Day 7: 12:00 AM - 1:00 AM - S7-E17
Plot hole: Jack is informed that experimental treatment using stem cells from a genetically compatible donor is being developed that might be able to cure his condition. Stem cells are used to treat diseases where a cell type in the patient's body malfunctions, such as insulin-producing beta cells in diabetes, or where injury has killed cells that do not regenerate, such as in spinal cord injury. In these cases stem cells can replace the damaged cells and make sense as therapy (bone marrow transplant as leukemia treatment is one real such treatment). Prions (which is what the show calls the bioagent) and bacteria (which is how the show describes the bioagent) cannot be cured by stem cells, since the cause of the disease is not damaged or defective cells. Even if the disease damaged brain cells and stem cells cured that, it would resume later since the causative agent is still there.
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 ★