OK, here it goes -- First, our dd is a pitcher now entering 18U. We've learned a few hard lessons. The biggest one -- don't rely on the girls to tell you if they hurt or are sore. Watch her, if she's doing or moving differently than normal, even if it is just a slight difference, chances are she's hurting and is adjusting so she can keep playing. These girls are tougher than nails and will do anything to stay on the field. One of our dd's teammates played the whole year with a broken wrist (throwing side) and was a pitcher as well. She just kept wrapping it with athletic tape and insisted it was "just a little sore."
Our dd has gone though rehab for three different injuries in the last 5 years, and we've taken her to nationally respected youth sports medicine people. They have told us the following: young pitchers 13U and younger should never pitch more than 80 to 100 pitches a day and never 3 days in a row. As the girl's bodies mature and get tougher they can go longer.
Our dd's first year of pitching fulltime was 14U. Several of the pitchers fell through, and the dd ended up the primary pitcher. The defense wasn't that good either, so she regularly had games with 150+ pitches. (one inning that defense gave up 11 outs and 80 pitches). The result was an overuse injury to her back -- compressed disc. The injury happened in late June, and it wasn't diagnosed until November after fall ball. She played with it, thinking it was just a sore back muscle.
If you are a pitcher's mom or dad, never allow your dd to be placed in that position. Each team should have at least 3 pitchers. Don't look for a team where your girl will be the No.1. Every year, our dd started out as the lowest pitcher, but ended the year as the No. 1 because she competed. I was never prouder as a dad than when in her 1st year of 16U she joined a team with a dominant No.1 pitcher. Halfway through the season, the other girl told her, "I'm a good pitcher, but we always win when you're in the circle."
Through it all, she's learned to listen to her body, works on getting warmed up properly, and knows what will happen if she isn't properly loose. But until you can trust your dd to know that, watch her. If you don't, chances are nobody else will and that includes most coaches.
In the old days, coaches would find one horse and ride it all tournament and all season. It doesn't work that way. Even the seemingly indestructable pitchers will break down from overwork, or just not tell anybody.
One of her favorite picthing coaches told her, "It shouldn't hurt to pitch. If it does, something's wrong."
Sorry for the sermon.