Running behind myself, Harriet wrote (about Arlen):
She says she's an officer. Possibility: A bright young cadet is told "Kill Blake and smoke out his rebels, and there's an instant promotion for you." She's done it (with a little help from his friends), so she assumes the promotion.
I can't see them using a cadet for such an important job. They'd want a fully trained undercover officer. They don't want an untrained cadet who might mess up, get caught and give away that the Federation is hard on Blake's heels.
Cadets are cadets for a reason; they are being trained to be future officers. So I can't see the Federation "wasting" a cadet by throwing him/her into a situation for which she/he isn't prepared, either. My knowledge of the military is pretty spotty beyond a certain amount of knowledge about the present day U.S., but officers (here) are trained beyond the basics of military academies and/or OCS before they are given the type of responsibility Arlen has on GP. So I don't even think Arlen is a fresh-faced newly commissioned officer. She's been around, and she's proven herself to be brave, reliable, resilient, and clever. (IMO)
Carol