it's really not that uncharted for Callahan. In Callahan's first season he kicked off All American bound center Richie Incognito off the team because he was being a complete jerk and distraction and breaking team rules left and right. This was at a time when O-Line was a huge weakness of ours at the time.
I think regardless of what he does he's going to get hammered by people. If he doesn't punish Mo with what appears to be a stiff penalty, like if they decide to handle it internally, whatever that is, then he'll look like he just wants to win, and if he kicks him off the team, he'll look like a jerk. I mean after all, it's just a barfight.
By the way, it's sounding more and more like she jumped into the fracas and was hit by a punch that was not meant for her, like a hockey ref trying to stop a fight.