Lift the couch and look at the feet- was it a screw, staple, stone, glider that scratched it? Personally, I don't think scratching a floor should be possible with a new sofa, because it should come with non-marring feet.
If the floor was recently finished and you know what was used, get some of it, sand it down and put a few coats on, letting them dry according to the directions.
Best plan- take her away for a long weekend or a week and arrange for someone to go in and repair it while you're gone. Make sure they get all of the odor out. Good as new and she'll never know.