...I don't think she would be killing for it unless she did truly believe that was the case. It's possible that it is true, but if we already know that some of us can be influenced into going that far...

I don't know. Maybe she wasn't willing, and had to be-- forced to believe she was truly helping. Byleth confessed, but she wouldn't give her motivation; they might have been blocked to prevent us from realizing something was wrong.