Out of curiosity I just did a search on my dream journal. Turns out I dreamed about a mirror only once… Walked into a bathroom and the mirror was all steamed up like someone just had a shower. When I wipe the steam off the mirror I see a camera behind it.
Remember feeling particularly paranoid about mirrors for a few days after that dream! 
There are only two options in my dreams for when I look at myself in the mirror:
I see myself as more beautiful than I think I am IRL, as in, I have longer, curly hair, am thinner, wear more fitting clothes.
I start feeling dizzy and watch myself spit out a lot of blood.
Sometimes both of those.
In a normal dream about work, I realized I was in a dream, ran to the bathroom to
see what my dream body looks like. Well, for a brief few seconds a thousand different faces of all genders and races flash before me. The last face was fixed , stayed in the mirror, was of a black middle aged cheerful looking woman. Never saw my physical face. Am thinking I was shown the faces from all or most of my past lives.