Katniss is used to some pretty unconventional-looking soldiers, especially coming, as she does, from the side of the rebels. Everyone age fourteen and over was considered part of the army and trained as such.

Prim was thirteen. That didn't protect her.

Her eyebrows rise at the question. "I don't think I need to be blowing up any of my own fingers anytime soon." ... well, she might. She runs her fingertips along the edges of her bow like it's a security blanket. "I used to have arrows with explosive tips. A friend made them for me. That could get..." Her mouth quirks upwards in a half-smile. "Intense."