Rachael is a factory worker who was childhood friends with Stephen's wife. She is now in love with Stephen, and helps him deal with life as a friend. After Stephen's death, she spends the rest of her life taking care of his widow.
Like many sidekicks, Rachael is kind of a one-note character. She is patient, long-suffering, giving, nurturing, and selfless…. She loves Stephen, and Stephen loves her. Sadly, they can never be together, because he's married to a belligerent drunk. Rachael is far too classy to go for an out-of-wedlock scenario. Instead, she lives a reasonably miserable life as a lonely factory worker, takes long platonic walks with Stephen in the moonlight, and spends most of her life after he dies taking care of his widow.
Why do you think Rachael was included in the novel? Why not just have Stephen and his wife, and their horrible marriage, without this other woman in the picture? Also, why do you think her fate is to deal with Stephen's wife? Why doesn't she get to move from that whole situation to a life of, say, marriage and children?