Answer: Why did Mrs. Hadley, who had been so frightened of the nursery, urge George to let the kids have it on for one last time? Hadley believes that even though the nursery is becomingly terrifyingly real, just a few more minutes can't hurt, because she thinks the main damage has already been done.
Your keyword is "nonessential" which means you don't need it. So the statement is true a nonessential element is not necessary for the meaning or the structure of the sentence.
