To best support your argument against Kiara's claim that the first piece of art ever created was a sculpture, you might say:
"Time, natural elements, and other forces have erased most of the early art from the Earth, so we may not ever know for certain what was the first piece of art ever created. Additionally, prehistoric art includes a variety of forms, such as cave paintings and carvings, and without written records, we can't definitively say whether sculptures or paintings came first."
This response acknowledges the uncertainty surrounding early art while pointing out that both sculptures and paintings existed in prehistoric times.