I've had my position for about 12 months and having recently been accepted to a graduate program (unrelated to my current career). I've been planning to leave for some time (approximately 2 months from now) but I have not yet told anyone about my plans to leave.
Recently, I learned that a co-worker who started in my same position about 3 months ago was just promoted over me, but in secret. We have similar educational pedigrees and prior experience and I've helped her out extensively on several projects. She does a fine job, but understandably needs some hand-holding given that she is so new.
Although no one in the company was notified of her promotion (and ostensibly I am not supposed to know that she is now more senior than I), it has become quite difficult to work with her since its obvious that some of her new "seniority" has gone to her head. She consistently challenges me on elements of projects that it is obvious she has no idea how to do. I did some reconnaissance with friends in HR and they told me that she was indeed promoted, but management made a decision not to make her promotion public, implying that it was an attempt to preserve my morale. Additionally, she has not been particularly private about it, updating her e-mail signature with her new title.
I'd like to keep working for the next few months until school starts, but this situation has made it quite difficult. Is it worth bringing it issue up to management? In the best case scenario and I'm promoted, how bad would it look to quit in a couple months for school? In the worst case, is it likely I would be fired for discovering this?
TL;DR Coworker is promoted in secret. Now bosses me around but is clueless and I'm not supposed to know that she's actually senior to me. Quit now or leverage for promotion and quit later?