In my opinion, this girl expressed the narcissistic personality traits. She feels superior in general, and that's the reason she didn't do anything, but questioned your work. And she attacked "the other idler" because she had to put the blame on him. If you are interested, read some articles about narcissistic personality disorder and you might find similarities with this girl's behavior.
I never thought that such personality disorder exists. Thank you for sharing this. Too bad the treatment is not well studied, have to find more information about this.
Well, the treatment is a very long process, but often not successful, because those people usually are not able to acknowledge that they have a problem. If you continue exploring the subject you'll understand why is that and how they really feel. .... You are welcome. :) Keep posting good stuff!