According to the film script it's actually Captain Deladier who is the Instructor. Zander is merely Ibanez' supervisor and a lowly second Lieutenant to boot, a rank that Ibanez evidently secures as soon as she qualifies as a pilot, a few weeks later:
ATHENA - COMMAND AND CONTROL - DAY CYCLE - CARMEN arrives on the bridge, dark, cramped, all-business. She salutes the instructor, CAPTAIN DELADIER, 40s.
CARMEN: Pilot Trainee Ibanez reporting for duty, ma'am.
DELADIER: Take the number one chair, Ibanez. Follow all instructions of you supervisor.
CARMEN: Yes, ma'am!
Carmen turns for her station, but stops in her tracks. Her supervisor is Zander Barcalow, now a 2nd Lieutenant.
Since Zander was already shipping out when they were finishing high school, it's certainly possible that he attained his rank in much the same timescale without the need to construct elaborate theories about him already being at Flight School but for some reason still playing High School football.