Las Vegas—at least the casino studded Strip—was luxurious. Finding high-end jewelers to buy gems wouldn't be difficult. What would be was getting the gems in the first place.
Ruby's powers didn't work unless there was dirt or stone beneath her. Concrete or asphalt, manmade items, wouldn't cut it. She couldn't exactly make a bunch of gems shoot out of the ground in a public park either; she needed to go somewhere secluded.
She ended up taking the car she rented out to the foothills and finding a nice spot far enough from the road that she wouldn't be seen. She had brought a large bag with her to put everything in so she would hopefully only have to do this once while she was here.
Hiding it would be simple enough to do; Ash wasn't a snoop. He never once bothered to go down into the dungeon and see what she was working on when she was fixing up the windows. She was certain he would have said something if he had.
