The killer getting away bothers me to the core, and the brother is a damned coward for bringing an armed buddy to a fist-fight. From the article, it appeared Kat's brother didn't do much or any talking at all.
I don't think Kat deserves the murder charge, since she only sic'd her brother on Mike. She may not have known that he would bring his murderer buddy with him, or at the very least had no direct control over their actions. It's clear that she's trouble, but if you could convict girls just for being trouble-making bitches, well... there'd be a lot more bitches of the female persuasion in jail.
The entire situation is regrettable, but the fact is that it's inevitable that a story like this will pop up again. It happens all the time and is usually resolved with little more than words or a minor scuffle, but every now and then some idiot looking with something to prove brings a weapon of some sort. With all the idiots running amuck in the world, this sort of stuff is just bound to happen. People have been killed for less, really.