@antopatriarca @ojs - It's so thought-provoking!
Here's my impression of the painting. In the reflection she seems to be serving the man. In the direct view, she seems to be facing me. And this adds an excellent extra layer to the overall symbolism. The barmaid is forced to be "two-faced": to be a good barmaid, she has to make every customer feel special, as if she's only serving them.
In *reality*, for this scene to be possible, she must be no longer serving the man, and already facing the next customer (the painter/photographer).