I’d make double sure, even triple sure, the the one sconce provided the optimal lighting one would need in a bathroom before I nixed adding a second to save money. Because a lovely renovated bathroom that isn’t functional because a lack of good lighting will cost more in the long run (maybe not in actual dollars but in ease of use or even in actual dollars if you decide to add light later on). I’d save money on a cheaper sconce, or cheaper towel bars, no art, etc.

Could you just put a light bar above the mirror instead of a single sconce? They are very affordable and you won't run the risk of low light or having it look odd. This one is $70 at Lowes:

One sconce won't look right at all. Either buy less expensive sconces or follow the advice of Olychick above.

I actually prefer an light bar above the mirror to sconces .

Your daughter will need either two scones on either side of the mirror or one large light fixture above it. This will provide adequate light for make-up application. Anything less lacks function. Put out that extra bit of money - you won't regret it.

The sconce would be purely for looks, not actually lighting. (There will be several recessed lights in the ceiling above the vanity, and another decorative ceiling light as well.) I’ve always liked a lamp near a bathroom sink for low lighting/ambiance purposes. So that would be the purpose of the sconce. It would also be on a dimmer so that it could be used as a night light. Here’s pictures of the idea I have. One of standing inside the bathroom in front of the vanity and the other is the view from the door (which is inside the bedroom, and the other door in this view is the door leading into the tub/toilet area) Thoughts?

Please keep in mind this is a computer program and images are distorted. The decor, cabinetry, etc. is also just for the purpose of getting a visual of my design thoughts. The bathroom is currently an empty shell. :-/