Based on what you wrote, you're almost certainly a great parent, but I have a question:
If your daughter learned by observing the boy using a tantrum to get his way, couldn't there be other children who observed both the boy and your daughter, see that a tantrum at the very worst amounts to a 50% chance of ice cream and a 50% chance of continuing the zoo trip?
If you had told her: "When you're done, let me know. And if this goes on much longer we're going home once you're done." The other children may have observed possible negative consequences for their actions.
If your daughter learned by observing the boy using a tantrum to get his way, couldn't there be other children who observed both the boy and your daughter, see that a tantrum at the very worst amounts to a 50% chance of ice cream and a 50% chance of continuing the zoo trip?
If you had told her: "When you're done, let me know. And if this goes on much longer we're going home once you're done." The other children may have observed possible negative consequences for their actions.