3 going on 13

Tonight Emma and Natalie were playing in Emma's room. They were being especially quiet so I went to check on them. I found the door locked. I knocked and told Emma to open the door. She did. They were only playing with play jewelry. I told Emma that we never lock doors in our house and that she needed to leave the door open. As I turned to go back downstairs, she closed the door. Mumbling to myself, 'What part of leave the door open do you not understand?' I opened the door again and told her the door had to stay open. Her response, "We need the door closed and I just won't lock it anymore." I again told her the door had to stay open and compromised and pulled it 3/4 shut. She said, "But how about I just don't lock it?" WHAT?!? Who are you thirteen year old? What did you do with my three year old??