This wasn't 'discipline'. To discipline, you need to have self discipline.
This was loss of temper, and of self control, and lashing out at the most vulnerable target, as a result. The target, incidentally, being a creature that she had a duty of care towards, and to ensure that the creature did not create a hazard to other people, that she failed in. She failed. Not the horse. Not the hunt sabs (and I'm extremely lukewarm on huntsabs). The one that seriously fucked up here is her, and it's a shame that she was not able to deal with her fuck up in a more constructive, and less destructive manner.
She is/was a Big I Am in Pony Club, not a child who should have been taught better, and could be educated to do better. She is/was the educator.