Office Etiquette / Advice

[Nat]

I'm starting this thread because I'm seeking answers from those who know the rules of office etiquette better than I. But I hope others also can post their questions and advice here too.

Here's mine:

Okay - I have a small convex mirror (bigger than a quarter, but still relatively small) adhered to my monitor so people don't come up behind me and scare the bejeezus out of me. I have been at this job about a month and a half, and a woman who has been out with an injury just came back two days ago.

Today, she asked me why I had a mirror on my monitor, and was it so I could see what she was doing on her computer (she sits behind me, but the door is also behind me). I said, no, the mirror is too small for me to see anything she's doing. I tend to jump out of my skin if somebody approaches me from behind and I don't know they are coming. I asked if it bothered her, and she said, "yes, actually, it does."

I don't want to remove my mirror. I did move my monitor so the mirror doesn't show her in its line of sight, but now I'm getting a crick in my neck.

SO: Is my having a small mirror on my monitor a breach of office etiquette? Should I take it down out of consideration for her feelings, or will this encourage her to make future unreasonable demands? Have you ever been bothered by somebody in your office having a mirror attached to their desk, monitor or wall? Am I being an ass?