I like option 2 because it makes sense to fill the whole wall because of mirror issues, as you said, and I think a 56" vanity provides a nice amount of counter space. The shallow cabinet in front of the door will help the room feel less cramped, and I agree the wall mount vanity will help too. If she can live without solid surface, there's lots of formica out there that could look really good and modern without breaking the budget. I am in the process of a bathroom remodel, and also have the marble-look floors. I ended up finding a quartz remnant that is almost white, with just slight veining. It looks great with the floors. I had to look pretty hard to find a remnant, but it can be done. I'd say I probably saw an equal number of 2 and 3 cm remnants. But definitely finding granite remnants is easier, and black might be a good option.

I would use a roller and a brush. The roller would be first, followed painting areas that the roller didn't reach. Look for the Whizz roller systems. The are very small and the sleeves are narrow in daimeter. 3" would probably work. Those paint mitts seem like a good idea in theory, but are probably better for staining than painting. There could be any number of reasons for why the paint is not sticking/covering. Is your primer completely dry? Are the cans of paint shaken/stirred well? Sometimes if not stirred up, all the good stuff is at the bottom and the top is just solvent. It could also just be a poor covering color or product. There are disposable sprayers, but often you have to thin the paint so much to get the paint through, it's not really paint anymore.

So sorry I never updated this thread (such a bad habit to not conclude threads in case they pop up in future searches). I posted the tile info in another thread, but i should post it here too. The 'marble' tile is porcelain and is called Exedra Calacutta. 18 x 18 on the floor, 9 x 18 on the walls. The feature tile is Danse Lucido Vetromarmi collection water jet tile with glass and calcutta marble. The subways and shower floor 1 x 1s are Pavarotti Pearl. All tile is from Artistic Tile. BlackChamois the Gray Owl didn't work at all. All the ones I thought would be great just didn't look the same in the space. Enduring, we LOVE Smokey Taupe. It's our whole kitchen and library area paint. I just didn't like how it was pulling out the strong yellows in the tile. Maybe because the tile is porcelain and I felt it made it look more like porcelain and less like marble? In the end we stuck with Moonshine. It ended up settling in much less blue and much more green. I must have caught it in very specific light for it to look that blue. Paint is so tricky! Anyway, here is a link to the updated thread so I don't have two running at once on the same topic. Here is a link that might be useful: Sneak Peak of UNfinished Master Bath

I think it will be stunning in the cognac. I'd do it in a heartbeat and I love all your choices.