In "Good Country People" O'Connor comically and morbidly deals with humanity's religious confusion to portray everyone as grotesque: the Freemans, the Hopewells, and Manly Pointer. Namely, O'Connor focuses on Joy/Hulga's desire to be ugly, her lack of spiritual vision, and her wooden leg as a fetish of earthly materialism and sexual deviancy.
Look at the way O'Coonor describes Joy/Hulga physically:
"...the girl [Joy/Hulga Hopewell], standing square and rigid-shouldered with her neck thrust slightly forward, would reply, 'If you want me, her I am -- LIKE I AM'"
Perhaps it was the arthritic neck pain from which Miss O'Connor was afflicted, a contortion which doctor's call "Swan Neck," that so aptly serves as the site of spiritual interruption in her characters. Or maybe it was her training as a satirist and caricaturist, one who enlarges the head, dangling it off the weakened neck and shrunken body to serve as both a comic and grotesque symbol of conceit. It is with intended humor and pity that Hulga stalks instead of strolls and leers instead of speaks. Her head carries her body around like baggage (Joy/Hulga drags around a prosthetic leg). It would seem rational that her head should seek the requisite humility her body demands, but Miss O'Connor spitefully swells it for the sake of comic mismatch.
In "Flannery O’Connor’s Religious Vision of Regime Change," Charles and Leslie Rubin write:
O’Connor writes that the grotesqueness that appears in her stories is not rooted in the individuals she describes but in modern society, which is grotesque and distorted. What seems to distort social life in the stories is believing in explicableness and universal lawfulness, which reduces everything we can see to what we can explain. If there is uncontrollable evil in human souls, in apparently ordinary human beings, then hope that mere humans could establish social peace is misplaced. Such a misplaced hope can have fatal consequences.
So, Joy/Hulga's mislplaced hope in her nihilism and PhD gets exposed by Manley Pointer's cruelty. Without her leg and her degree, Joy feels helpless. She no longer can hide behind or literally escape her fallen state.