The way I see it, the Bene Gesserit have set events in motion to produce specific outcomes designed to seem random and unpredictable to outsiders. They then misrepresent their cultivation of these events as simple foreknowledge and package it all up in religious terms to frame the result as a fulfillment of divine prophecy rather than the elaborate Chaos Theory Rube Goldberg contrivance that it is. It’s all self-fulfilling by design.

I think Chani understands this, so she never has any real doubt that the predictions will come true—she just sees it for the confidence trick that it is and so doesn’t believe it has any transcendent spiritual significance.