I have to agree with Lt STOP with the treats, Horses are smart and when you start using treats they figure out what they need to do to get them, She will become mouthy and pushy. It is just time and working with her. I am a firm believer that a horse needs to stand tied (tie them comfortably). I don't care if they dig a 8 foot hole. It teaches them patience. I will let mine stand tied in their stalls or out at the fence, or by the trailer for an hour or more when I am working outside. I had a filly that I showed halter when she was young and she had a problem standing still when we were in the show ring. So i started tying her everywhere. At first she would paw and dig big holes, I just made sure where ever she was tied she couldn't hurt herself. It took time but by teaching her to stand tied quietly and then working with her and using a key word she finally got to the point that when we took her to the show ring that she would stand there quietly and sometimes fall asleep. It is time and patients and no treats.

Good luck