Although she gets less attention than the woman with the protruding teeth, this lady is quite opinionated. When Julian's mother mentions that they have the bus to themselves (without black passengers), she says, "For a change. I come on one the other day and they were thick as fleas—up front and all through" (51). Niiiiice.
She again makes her strong opinions known by moving seats when the well-dressed black man gets on the bus. The point? We're thinking that O'Connor uses these small moments to show us that there are people who are much more closed-minded than Julian's mother.