This is interesting. I've never seen a ball hit 300' but 3 girls on my DD's travel team have gone yard in a game. Farthest one was pretty darn close to 250' and another one that would have been if hit higher it was a line drive 215ft fence. But you're right most have not hit one 200' and most don't. Yet I've been at those 12U tournaments where I hear a guy saying that some team hit 6 out in one game.
What age group is your DD's team?
I think it would be possible for a 12U team to hit 6 HR in one game, but it would have to be special circumstances. I've never seen it. I'd think it would be a national-level team on a 200-foot fence or even shorter. When I coached 12U, we had 2 girls who could hit it out, but they never did in a game. And we were just an average team. I can envision that a really strong team could attract several guys like those 2 or even better and put on a show if the stars align.