She is apparently profoundly ashamed at being at Southerner and a Christian. She feels a need to prove that she isn't "intolerant" or "judgemental".
"She is apparently profoundly ashamed at being at Southerner and a Christian."
That is exactly what I thought - she doesn't have the conviction to live the way she was raised at Yale - so she will lash out at it. Nothing like a rebellious college kid.