Slave System, Why Is the Beast-Eared Girl the World-Destroying Witch?

[Western Fantasy + Time Travel + Single Female Protagonist] On the first day of time travel, I was bound to the slave system. The system sent me a silver-haired girl with cat ears. She is afraid of strangers, silent, loves fish, and trembles when I get hurt. I thought I had picked up a poor one. Until she looked at him, half of the royal capital was gone. System prompt: Your slave is returning to the form of destruction. Me: Is it too late to return it now?