Smoke In the Air

Sam and Dean met Cat Violet when she was six year old, and when they still believed in Santa Clause. They were close, friends even, until one day, Cat decided to run away, and out of their lives. Years later, they meet again. They reconnect, and it's just like old times. Except Cat refuses to tell them why she left. What was so bad to make her run away? *Takes place in season five