It's no fun to storm off to your room if no one comes to get you. Tell her that taking a time to calm is ok, but that you are sending her friend(s) home after ten minutes if she doesn't come out of her room to work out the issue (set this up beforehand). When she storms off to her room, don't let anyone cajole her out....she's a stubborn one, she'll call your bluff and and possibly up the ante. But it's crucial to not give in once you set the rule...even the slightest give in will reinforce that she must act up even more to get her way. Unless she is at serious risk of harming herself (more than head banging and punching walls), let her come to you. It will be a no fun process, but she'll at least change the room stand off. "Transforming the a Difficult Child" is a great resource to help you
