How to make a pony not be mouthy?

Clearly you have given her to many treats in the past and she's just doing what she usually gets rewarded for. We are all guilty of doing this, but it can be highly dangerous as horses are large and dangerous creatures. Carrying a whip to pop her on the nose with is most effective with a sharp noise. Don't take treats with you for a while. Instead place them in her bucket. You would much rather have her harassing some plastic than you.