I do I mean really do understand how when people come up behind you and say nothing in the office can make you jump but at the same time I would be paranoid of a mirror being directed at me. Weather you are looking or not or can see everything or just a gesture I would feel like I am being watched and not because I am doing anything at my desk I am pretty boring. LOL Kind of like walking a park and someone walking behind you step by step.
I guess you would have to see it in her eyes that she has a mirror directed right at you and can see maybe not everything but the basics.
It is for your peace that you are doing it maybe talk to the coworkers so they can come in your site and not behind you every time they need you or maybe see about moving your monitor and chairs and all. I am not sure if you have the desk that goes all around or just in the front. Just thinking of ways to make both of you happier in the work place. I guess by compromising.