The climax comes during the scene where the wandering salesman, Manley Pointer, steals Hulga's leg. The irony in his evil, and her reflective innocence, reveals that Hulga has been trapped by her physical incapacity, as well as her spiritual.
This is the moment when Hulga's carefully built defense of nihilism breaks down. Instead of being the temptress, soiling a God-fearing man as she supposed, she finds herself the victim of an act of violence and cruelty. All of her supposed intellect and crafted belief in nothing is revealed to be just that: nothing. She finds that someone else has essentially come to the same conclusions, with none of the advantages. Instead of rejecting her roots, and transforming herself into something ugly, she should have kept the spirituality of the "good country folk."
There is a chance at redemption, however. Having lost her leg, she has lost her outward symbol of defiance and denial. She can now explore the possibility of returning to a relationship with those around her, including the spirituality needed to be whole.