Simple way to fix the debate. Have her take the sign and slip it into her bra strap and take a selfy.
First off their is no other black parts, just darker pixels and we know it was photoshop, no one will judge you if you just say it, but don't lie and say it isn't.
What color would you say is the thing to the right of the sign which appears to be the floor?
I'm not lying. I didn't photoshop and I know the model doesn't have the skills to do it. She takes sign pics all the time so there's no reason for her to photoshop it.