"...I fit your idiom well? What does that mean?" She bites back the even mean, but it's still in the tone, as much as she wishes it hadn't been there.

She's not going to point out that her being herself won't help him very much. She won't be able to do much, only hide in the shadows and hope to remain unseen, and somehw survive. Let him believe that she'll be useful, that is important.