By the time the body shop buys the bumper from Nissan, adds their markup, pays somebody to remove the old one, paint the new one then install the new one, I’m not surprised it comes out to that much. Any of us would simply just leave the scratch or paint the old bumper. However, since the person who got hit probably knows nothing and cares even less about cars, she will do whatever the mechanical tells her. In this case, get a new one. Plus she doesn’t have to pay for it.
You are better off paying it and not going through insurance since you will get raped for having an at fault accident.