Oh my gosh, that is horrible. I hope she heals as well as possible in her situation.
Although there can be situations when a fight has to be stopped, if possible. At a barn I worked, an unsupervised teenage helper accidentally let a stallion loose in the barn and it went to have a fight with another stallion that was stalled. I ran there when I heard the commotion and the stallions were at a very serious risk of injuring themselves and crashing the stalls. Of course, I didn't go between them, that could have been lethal, but I hosed the attacker off with a strong hose and ice-cold water. And that's the only safe (if you know what you are doing and place yourself in a safe position) way I can think of to stop a fight, if needed... Also, cracking whips or making other sudden, loud noises, as the previous poster suggested.
I have come a long way, to surrender my shadow to the shadow of my horse.