How is Kate different than the other walkers in the novel, The Unlikely Pilgrimage of Harold Fry?

Kate is a young woman who is recently divorced when she joins Harold on his walk. She is sincere and seems to believe in Harold even when other walkers are self-serving and manipulative. Kate remains with Harold when everyone else leaves him but she then announces that she's going to rejoin her husband. Harold knows she has to go back to her own life but he feels a connection with Kate that he doesn't feel with anyone else.