One light over the mirror is the best.

I would say do a slim vanity light. Do you have pictures that you can share?

Linear light over the mirror. Scones will just bring attention to how narrow the room is.

I agree with both of ya'll! I am a huge fan of sconces in a bathroom setting of a vanity light, but the size of the powder I think will make the space seem so closed and play the enemy to something that usually gives a great experiences. Good luck!

While I don't know the exact dimensions of the narrow powder rooms above neither looks "off" or crowded by the sconces. On the other hand, try to imagine an over-the-mirror fixture in either setting : [ My vote is still for the sconces.

One thing I would add is look how the whole wall behind the mirror is the same tile or wallpaper. This gives the tiny rooms a nice continuity.