The deal is that kids at her age can have terrible form and pitch well. So, she goes to some games and sees some other kids throwing and she starts incorporating what they are doing into her motion...she doesn't necessarily "intend" to do it, but she does anyway.
You have to keep going back, over and over again, to the basics. You have to drill it into her head the right way to pitch...which is:
1) Good posture.
2) Good leg drive.
3) Brush interference
4) Internal rotation.
5) Front side resistance
Sit down with her, and go over what this means.
Then, pull out a video of her, and let *HER* grade one of her pitches for each of these 5 things.
Your goal is to teach her the hows and whys of pitching.