An interesting thread brewing on the forum this morning, kicked off by some points made by Xzzy concerning Cortana's whereabouts during the section of the storyline we've recently been exposed to.
Essentially, there is good evidence that Cortana was on the Pillar of Autumn during its decoy mission, and Forensic cites the fourth Cortana letter in stating that Cortana and the BW-AI Class III artificial intelligence that appears to belong to the ship. Interesting reading, and your thoughts on the matter are welcomed.