You know how most people expect better behavior out of gifted kids because they talk better? I think this is like that. People think it's ok to let the good smart kids think they should judge what other people are doing, (or else how can they think for themselves, I guess the logic goes). (or maybe the logic is I see no way to stop it, and technically the kid's right). So the adult answers usually fall into "you're right I'll fix it." or "You're right but life's not fair, deal with it."
My answer is more in line with the bumpersticker "quit yer bitchin' and start a revolution". I guess my answer is that I file it under complaining. Why are you complaining? I hate complaining. We all complain a lot anyway (me, the hubby, and the kids).
Sure you can have opinions or gossip with the adults about other children, but don't get upset that you are not in charge of the other children because those are not your children and you are not their mother. Again, ALWAYs tell and get attention if somebody's going to get hurt or break something. But other than that focus on the things that you have control over and you'll have your hands full enough with just that.
My son believed me when I told him this about the other kids, but I can't get him to understand that this applies to his sister too. He still wants to manage her behavior. He and I argue about that very thing all the time. I yell, "How is SHE ever going to learn to listen to ME if YOU don't leave her alone and let me and her work it out?!" I'm so mad about that. It's very frusterating. I think he's just as mad that it looks like his sister's getting away with something. How can I discipline her anyway if he's right in the middle of it, center of attention, as always. And you parents know disciplin is not a two-second on the spot thing, it takes a few minutes to play out. For example if I say "Stop" she needs at least a few seconds to choose to stop or not. We need a few moments for her to understand that I mean what I say. We need several instances for me and her to work out the dynamics. I tell him, give your sister some room to get in trouble. You never give her a chance to get in trouble.
(crazy arguement, huh?)
Hopefully that analogy shows you how, in a way, the coach is right and your kid is wrong. In another way the coach is just doing a less than stellar job and your kid's calling him on it, but that's not the most productive fact to grab from the events.

By melting down your kid is hogging the opportunity to act foolish and not letting any else have a turn at being the biggest fool. What's more, since gifted have a rich inner life this meltdown and acting foolish might be only playing out inside her head. You never said if the meltdown is on the field, but I'm suspecting it's only happening verbally afterwards with the context clues "super angry" and "therapist" I'm not envisioning two year old temper tantrums, but a more wordy and sophisticated version of the same feelings.

I don't know if I should even post this because I'm unsure if it's helpful or even relevant, it's just thoughts. That's one trait my thoughts have is always drawing parallels between unconnected issues. Out of all the gifted traits lists I've read, that's the one that sticks out like the biggest sore thumb on me.



Youth lives by personality, age lives by calculation. -- Aristotle on a calendar