To answer one of your questions. No, the girls do not have to windmill. They can just take the ball back and release it as they bring it forward. Both feet, normally (according to local or ASA rules) must start on the pitching plate. I have a pic that I can send you.
On the same note, check with your local HS. Our town has 1 or 2 days of clinics (an hour or 2 at a time) run by the HS coach and staffed by the players.Since leagues always need more and better pitchers, maybe the league can set up a pitching clinic. A pitching coach may be quite willing to teach a 1-2 hour group lesson for $10 per student (or maybe even for free).