The Dark Horse by Marcus Sedgwick
When Horn's war party found the girl, she was hidden in the corner of the cave, undressed, and past comforting by the wolves who raised her. They had been slaughtered by the Lawspeaker's band or else run off, howling their rage and loneliness. A foundling, surely, filthy, perhaps seven or eight summers old. Horn, the Lawspeaker, growled that she should not join the Storn tribe. A worthless child... another mouth to feed in starving times.