The ONLY way to improve your game is through reps. Reps at a high level are great, but you have to be on the field to get them. My advice is go to the highest competitive team where she will consistently see the field during games. Practice is great, but games are where she needs the reps to get better. And I would def be worried about what she sees/hears in the dugout with 14-15 year olds. So if it was my DD, we would play for the highest level 12u. Good luck! Ultimately, it will be a learning experience for you guys either way.