Board Thread:General Discussion/@comment-33754845-20190916192846/@comment-27144409-20191129031918

And even aside from the moral reasons, her killing him would get her caught, and team RWBY wouldn't help her. She'd rot or be executed (without knowing Atlas' legal system), the SDC would go down in flames, RWBY would become RBY, and Weiss would be alone, hated by the world and her former friends.

Even if she was a heartless murderer, there'd be nothing to gain long term.