It looks like they just added a panel of the marble to the front skirt and then if you look closely at the picture it seems that the front of the tub is a bit higher than the back and that maybe they just added a small trim piece over the top edge of the tub and finished off both sides. They ran it wall to wall from what I can tell. Are there any other pictures?

Also, you can use plywood and attach the marble to the plywood and then use it as the front skirt for the tub. It would really depend on the lip of the tub as to whether or not you had to add a top trim piece.

Maybe not on the trim piece to the top. Looks like that is the tub and they just added the skirt. That is a great bathroom. Hope you can make it happen for you. Small bathrooms are hard sometimes. I think the plywood skirt with the marble attached would look great.

Thanks so much for the response! I don't have more photos but here are clearer close ups.

Thanks again, I'll let you know how it goes!