why kahu is a child of destiny?

Kahu is the heir apparent for the title of chief. There is no one left to carry the title after her great-grandfather dies, but he refuses to look on her in the capacity because she's a girl. None-the-less, Kahu has inherited the gifts of her ancestor, namely the (gift) ability to communicate with the whales, and it is her destiny to save the whale (the spiritual whale) and lead the others off the beach. Through this, her destiny as leader of the tribe is cemented.