In Flannery O'Connor's "A Good Man Is Hard to Find," why does the grandmother have an epiphany, and what is its significance?

The grandmother has an
epiphany, an illuminating realization of truth, because, as the Misfit identifies in the end,
she finally "had...somebody there to shoot her." It took being in a life-and-death
situation, a moment that tested all of her mettle and values, for her to have a realization
about her own humanity as well as the Misfit's. When the Misfit shows emotion and vulnerability,
his voice "about to crack," this is when her own "head cleared for an
instant." It seems that this is the exact moment of her epiphany: when she observes his
emotions in her own heightened emotional state, she realizes how they are similar, rather than
how they are different.

The Misfit is precisely the kind of person that the
grandmother would never have called a "good man" before she found herself in this
situation. He has been to prison multiple times; he's been accused of many crimes, some of which
he has actually committed. He doesn't come from a family she would consider to be "good
people," even...