The truth is, I'm betting the moms of the girls Julia complains about most would react first defensively, then try to make it Julia's fault instead of considering their girls could be doing something wrong. The article mentions the moms thinking of it as a sign that their daughter is popular and being happy about that.
So the moral of the story is this: Don't assume your kid never puts any other kids down at school. Talk to them about how it feels when someone is mean to them and how important it is to not do that to someone else. Also how awesome it would feel if someone took up for you when someone was being mean and how you can be that awesome person for someone else when you see them being picked on.