The scene of Eveline's epiphany, when she realizes in a flash that she can't leave Dublin with Frank, is substantial because of the ways Joyce communicates and emphasizes the emotional intensity tearing Eveline apart as a contrast to her outward frozen immobility.
Eveline does not make the decision to remain fixed at home in Dublin easily. She might be standing still amid the "swaying" crowd with her "cheek pale and cold," but inwardly she is in a tumult. Her emotions are in a violent upheaval. She is so upset that she feels "nausea" and her silent prayer is "fervent." Further, "A bell clanged upon her heart." Her emotions rise higher: "All the seas of the world tumbled about her heart." This hyperbole highlights her turmoil. She thinks wildly "No! No! No!" and feels "frenzy." We learn that:
Amid the seas [tumbling around her heart] she sent a cry of anguish.
Joyce makes it clear—and highlights—in the last line of the story that there is a disconnect between her inward pain and her cold outward demeanor as she faces Frank:
She set her white face to him, passive, like a helpless animal. Her eyes gave him no sign of love or farewell or recognition.
Joyce's epiphanies focus on the interior of a character's experience. On the outside, it can seem that nothing at all is happening, as occurs with Evelyn. Looking at Evelyn from afar, a stranger would only see that she is "passive" and doesn't seem emotionally alive at all—she gives Frank no indication of "love or farewell or recognition." What counts for Joyce, however, is psychological experience. He shows that while it looks as if nothing is going on, Evelyn is probably experiencing the most intense and heart rending emotions of her entire life.