Part of it might be wanting to keep her nude-modeling career separate from the rest of her modeling. If you look at the two Michelle McCurry links above, there are only a couple of nudes, and they're very "artistic looking". Mostly, it's just fashion-modeling kind of stuff.
I would guess that it's much harder to get mainstream modeling work if you've posed nude, and it's widely known. So perhaps Barbie/Michelle/Veronica/whatever is trying to keep her mainstream modeling career going, but she wants to make a little money on the side doing nude modeling, and she doesn't want the M&B stuff to interfere with her mainstream career?
That would explain why her agent is so adamant about denying that Barbie and Michelle are the same person. He's trying to protect her career.