Take a pic of the real space and post it . This is like it is sort of like this but different how can we possibly answer that.I would for sure look for a lit make up mirror instaed of sconces and ideally one with a magnifier on one side .That sconce in the inspo pic is totally usless .

This is the way the space looked before and currently. The new shower will come out close to the window. The makeup vanity will be under the window.

I don't think you should worry so much about two-sconce-balance. What you want is light. And if that is the only place for it, then find the best fixture that you like and put it there. If it is a bit larger, it won't look like a "lonely little sconce" but rather a wall light.

The one sconce will look fine, but If you have any room at all to the left of the window you may want to consider pendant lights hung from ceiling so that you have good lighting to put on makeup. If that’s not possible then just fine sconce.

A single sconce can look intentional here; symmetry is less important than how evenly the face is lit. For makeup, though, one small point-source sconce in the corner may create stronger light on one side of the face. I would use a taller, diffused fixture rather than a compact exposed bulb, and place it so the light reaches the seated face rather than washing only the wall.

If the window provides good daytime light, the single sconce can be the secondary layer. For evenings, consider a high-CRI ceiling light positioned slightly in front of the seated person, or another broad frontal light source, so the corner sconce is not doing all the work. Mock up the fixture size with cardboard and view it from the doorway before the electrician sets the box.

Thank you!! I bought this light fixture for the double vanity on the opposite wall and will be hanging two of them horizontally over the mirrors. Can anyone suggest a coordinating single sconce for the makeup vanity? It will be across the room.

I had considered that, but I wasn’t sure if it would look funny having the same fixture mounted vertically and horizontally in different parts of the room. Maybe I will hold it up and see how it looks. Thanks again for the suggestion.