Cortana's been in Navigation her entire (if thus far short) time on the Moira and has no intention of looking for another job. navigation is one of her particular talents and is something she did often in her own world. she'd run entire spaceships and navigate them not only through space in general, but also in the midst of battles. being an AI, essentially made of numbers and code, she's got an obvious talent for math in which it's nearly impossible for her to make incorrect calculations and errors in navigation are rare.

and since communication with the rest of the department is important when it comes to being in a head position, it should also be noted that she's quite the people person, too. despite being a computer program, she interacts with organic beings with ease. but, all the above said, she's also slightly rampant which has potential to cause problems here and there, not just in the social aspect of the job.