You can delete her computer from the network list, although she could reconnect.
Don't do it though. That's a bitch move. Call of Duty sucks, anyway. Used to be they literally built the game off old veteran's stories, and now it's made up stuff like everything else with crappy gimmicks.
isn't this piracy
Where does it say he's illegally downloading it? What about buying it off Steam or something and downloading?