Your best bet would have been to stay and train her when & where it happen (if possible)
Now......On the lead walk right up to the sheep, get them running so they catch the dogs eye, then every time she looks at them, lose your rag with her...don't mean beating the shit out of her, i pinned Khan to the ground screaming in his face ragging him when he caught one. Me angry scared him more than a kicking ever would. Too much beating can make a dog too scared to come back to you if it even 'thinks' you might be angry, and you will need to be able to recall it! But for any type of training t