SOLUTION: Have friend who is not emotionally attached to child's minutiae, but who has a child of her own (and is thus moderately compassionate to those sensibilities), volunteer to come over and clean said room. Do not hesitate when she asks for the broom and dustpan -- just get it for her. Do not pay attention to the crap that she sweeps up and deems unworthy -- just open the trash bin. (I did rescue a couple of sticker pages. ) Marvel at the tidiness that emerges when a dispassionate agent imposes order.
Thank her profusely and bake her a loaf of lentil bread.
(Laugh at daughter who asks, incredulously, "Why is my room clean?")