I highly respect coachp, but I disagree about bringing stuff from outside the gym into gym.
There is a girl on my daughter's team who does the mean stuff on social media -- the typical name calling, talking bad about people, childish stuff. I would never bring this to a coach and try to make the coaches police the behavior of another girl. I mentioned it once to the offending girl's mom, in a very low key I-know-kids-can-push-boundaries-as-they-grow-up-but-you-might-want-to-look-at-some-of-this-stuff way, and of course she went all mama bear and claimed her daughter was the victim. So, my solution is my dd blocks the mean girl on all social media and does not socialize with her outside gym, but is kind to her at gym. How would telling the coach help? I'm not going to have a coach tell me my dd must engage someone outside gym, and our solution works for us.
I'm also thinking specifically of a teammate who spent the night at my house a couple of times for group get together. She ended up stealing from my dd. We actually caught her; this isn't conjecture. That child is not invited back to our house, but I would never go to the gym and accuse another child of being a thief. It didn't happen at the gym, and I think it would be wrong for my dd to tell everyone at gym about it. I think even such an accusation at gym would create drama for everyone. I have never told another parent and I told my dd that if anyone ever asks why this child isn't at any future sleepovers at our house, just to say she was busy. I'm not sure the value in telling the coach that both girls share and have to trust?