Anger from nowhere

I will never forget last night when Brit was yelling at the boys to be quiet. She told them I was sleeping as she was kneeling on my bed yelling at the top of her lungs, all the while I was laughing hysterically. If I was asleep, why would she be on my bed yelling? Then she went downstairs and yelled some more from the downstairs window. Later that night when we were talking about throwing away a water bottle she thought it would be hilarious if we threw it at the boys. I don't know what has caused her to dislike our neighbors, but I find it hilarious!