Why did Annmarie behave like Kristi when she was stopped by German soldiers in number the stars?

Annemarie pretended to act like Kristi when stopped by German soldiers in "Number the Stars" to protect her friend Ellen, who was Jewish and in danger of being arrested. By pretending to be her younger sister Kristi, Annemarie avoided suspicion and helped protect Ellen by diverting attention away from her. It was a quick-thinking and selfless act to keep Ellen safe during a dangerous time.