My horse runs through the bit, how do i train her to stop?

Make sure you are using a bit that actually fits her and isn't causing problems, and don't go to a harsher bit to get the effect you want. Longe her and get her responding to you voice cues, like saying "walk" "trot" and "canter" . When she starts responding to your voice aids, get on her and gently apply light pressure to the reins while saying "walk" or "whoah" to get her to go slower or to stop. Also keep using your seat and keep your heels down! I hope this will help! :)