Isn't it deeper than just that? I'd say she's beginning to realise stuff like this can't go on and she should do something about it as a Whispered, not just remain a third party to be protected. And that something isn't what Mithril has been trying to do since she clearly hates Sousuke casually killing people. However, she wouldn't know what she could do, so she's both emotionally and intellectually locked down until she figures it out. She's rejecting reality and trying to come up with her own.