Is some part of this unclear? Are you trying to make a point? She came outside with the weapon, began hitting him with it. He took it away and began hitting her with the same weapon.
He was then armed with a deadly weapon and she had legal permission to defend herself with deadly force. Except that he would not have had the weapon if she hadn't been beating him with it first.
A few points, actually. One, nothing in the news reports say she struck him. Two, the dude had plenty options. He didn't have to rob her place. He didn't have to take the weapon, he could have chosen some sort of escape/evasion. Once he did take the weapon he could have chosen to thrown it clear of the altercation point or done something other than choosing to beat her brother with it. I don't think the perp would have been shot, or even caught, had he chosen to run back to the getaway car and told his driver to hightail it out of there at instant he saw the robbery going south, instead of later on in the game.