That's my fault

Just now, I threw Shelby's dolly up by her when she was sitting down to watch a movie in my bed. She was not in the best mood, and took the doll and threw her off the bed, saying, "I don't WANT that baby!!" So I told her that she was not going to get to do nice things like watch movies if she was going to be a gripey little girl. She said what she often says, which is, "Leave me alone mommy!" I told her that she does not tell me to leave her alone, I'm her mommy, etc, etc. She said, "Fine! I'm FINE! That's my fault." She's been saying that a lot lately. Where did she learn that and how do you respond to that?!?! haha