Wow! Talk about a thread I needed to see just when I needed to see it!
We are having similar issues at DD's gym and while it's never directly affected her, it seems the age difference in the group is the root cause. One teammate just cannot accept that the younger ones are 1) there, 2) given the same amount of time as the older girls, and 3) are quite a bit better than the older girls, even though they are lower level (not that they are superstars or phenoms, but they come every day, work hard, have positive attitudes, listen to and respect the coaches, and try to make the corrections they're given--surprised their skills are moving faster than the older girls who do the exact opposite of that last? I think not). The coach doesn't want to deal with it and has addressed the issue with the girls, but it still continues (just at a much quieter volume level). DD becomes quiet upset because her teammates are upset by the name calling and put downs.
I have told her she is right to stand up for her teammates, but ONLY if it does not disrupt practice anymore than practice has been disrupted. Parents of the targeted girls have addressed the issue with the coach individually as well. I just don't think it is possible to prevent snarky teenage girls from being, well, snarky, especially if they believe they are the best in the gym and should be catered to. As long as the coach is aware of the issue, the girls need to trust the coach to handle it.