I think throughout this excellent story that narrates the battle that occurs between Da-duh and her granddaughter, the most important moment and the climax of the story comes when Da-duh shows the narrator the highest object on the island in a last-ditch effort to try and prove that her world is superior to the New York that the narrator tells her about. As she shows the tree to the narrator that "appeared to be touching the blue dome of sky," and asks her if she has anything this tall in New York, note the narrator's response:
I almost wished, seeing her face, that I could have said no. "Yes," I said. "We've got buidlings hundreds of times this tall in New York."
It is after this, of course, that Da-duh begins to ail and die, as "all the fight went out of her at that." It is after this that she leads the way, and the narrator follows "triumphant yet strangely saddened" behind, as she counts the cost of the bitter victory that she has now won.