We would be interested in a 12u league too.
These leagues are fun for the ladies and a great way to challenge themselves. The leagues we participated in were called Winter H.S. Hitting league that ran from Early January to mid Feb 6 weeks. They were open to all ages and were comprised of teams of 4. If a player did not have a team the league director would take all ladies not on a team and form them. It was always packed because he also did boys baseball and Mens slow pitch leagues during the same time at $40 a team I am sure it was worthwhile for them.
My DD started when she was 10. She was on a team with HS age ladies and held her own. Scoring was done by a facility employee using a series of numbers on the back wall that the ladies tried to place the ball in.
All ground balls exiting the cage was worth one point and the ladies had to bunt the first pitch fair before scoring started. Lower targets and targets at the top were 2 or 3 points, 4 and 5 point targets were place in-between midway up the back wall. A swing and miss or foul ball or one in the box of the back of the cage was a 0.
Miami lakes had pitching machine balls with a little red seam, some were dimple and some worn seamless and with a seam.
With wheeled machines it created additional challenges for the hitters since they did not see many of the 12 pitches at bat in the same spot again and again. One machine was set to pitch between 60-65 mph the other between 45 and 50 at about 50 feet.
The last time we did a hitting league was 2012 and the league had 8 teams of four hitting on Sunday afternoons starting at 5pm, 6,pm,7pm,8pm. I know Tim also worked with some teams that had ladies that worked and could not make the early times so their team only hit at 8pm or, a player could stop in through the week and pre hit if she could not make a day.
League champs got T-shirts. I would think if you had a facility in your area and a couple organizations interested 6-8 teams of 3 or 4 ladies you could start a league pretty easy.