Yep, it was getting clear they had plans for Nina too and that she might as dangerous as Johan. She was introduced after all shooting her twin in the head. There was also the psychatrist she strangled under hypnosis, and her murder impulses ( a breath of fresh air compared to Tenma sparing everyone, let's get real for a minute, that's not daijobu).
Though, I hope the tables won't be completely turned. I don't want to pity Johan too much, no matter their circumstances, he's done vile things since childhood when Nina only wanted to live her life before being roped again into this.