What does Elphaba correctly deduce about the fish in the well of Kiamo Ko in the novel, Wicked: The Life and Times of the Wicked Witch of the West?

When Elphaba begins to fear spies everywhere, she comes to believe that the goldfish in the well of Kiamo Ko is the spirit of Madame Morrible. When Elphaba returns from Shiz following Madame Morrible's death, Liir announces that the goldfish died also, confriming her suspicions.