Veronica says all she wants is a dress, but it has to be nice and classy, like the pre-war dresses woman wore. Short of killing anyone in the Ultra-lux Casino, I didn't know where else to find such a dress. I put this quest off until I was strolling through the Sierra Madre in the Dead Money dlc. I came across 2 copies of Vera Keyes' dress. When I completed DM, I gave one dress to Veronica and kept the other for myself. Giving her the Vera dress completed the task of finding Veronica a nice, classy, pre-war dress. I like that I was able to do so without killing anyone for such an item.
On a side note, I play as a female character, (the reason I kept a copy of the dress for myself), and put it on. I looked at it on my gal in third-person view and held down the left bumper and used the right thumb stick to do a complete 360degree view. Wow, what a dress! If I were in Paris, I'd say, Ooh, la, la, la, la, la, la, la, la. Lol sorry. I had to rip off that song. Its was the first thing I thought of, though.