Daughter went through something similar. I would tend to think it is overuse. We did do a PRP treatment just as a precaution (They do cost some money). If it was my kid, I would probably recommend several weeks of rest from throwing. Let her play, but as a positional (low amount of throwing/DP) player. We had to end up taking off around 12 weeks from all throwing and playing (Mine would also have pain when hitting). Remember: Ounce of prevention is worth a pound of cure. I know you want to pitch her now, but you may risk a lot in the future.
Bill, yes I talked to our coach today and he is good with her at 1B for the rest of the season and will only put her back in to throw when we tell him she is good to go. This isn't the best time for her to be down, but we will deal with it to make sure she is 100% before risking additional injury. Thanks for the info on PRP.