The hurricane and the rabid dog are driving forces near the end of the novel that test Janie's mettle and ultimately provide her an opportunity to exercise her independence.
The hurricane causes Lake Okeechobee to leave its banks and floods the muck where Janie and Tea Cake are living. Literally, the two must run for their lives from the flood waters.
During their escape they encounter the rabid dog who attempts to attack Janie. Tea Cake, however, rushes to her aid but it bites Tea Cake in the cheek before he is able to subdue the canine. This, too, drives the plot's ending. Tea Cake assumes the bite is nothing more than a scratch but it proves to be much more and forces the end of Tea Cake and Janie's relationship.
Both of these events are beyond Janie's control. In fact, her only choice in these two situations is to respond or perish. This concept is what gives the novel its title. Before these events, as Tea Cake, Janie, and Motor Boat cower in the corner of their cabin trying to ride out the storm, the narrator tells us:
They sat in company with the others in other shanties, their eyes straining against crude walls and their should asking if He meant to measure their puny might against His. They seemed to be staring at the dark, but their eyes were watching God.
However, as sad as these events and novel's ending are in certain respects, the lessons Janie gains from them are essentially important. She learns self-reliance from these experiences and a degree of self-actualization as she reflects on the experiences.
As she tells Pheoby at the end of the novel, "You have to go there to know there."