Why does Anne Marie's mother tell her to act like a silly little girl if she is stopped?

Anne Marie's mother tells her to act silly is order to distract the soldiers..... make them believe she's harmless.

"Annemarie, you understand how dangerous this is. If any soldiers see you, if they stop you, you must pretend to be nothing more than a little girl. A silly, empty-headed little girl, taking lunch to a fisherman, a foolish uncle who forgot his bread and cheese."