Alienation, the state of being marginalised, isolated or withdrawn. It is a major theme in the novel.
Joy is alienated from society on several levels. We see her literal and physical alienation in the locations of her housing estate, Bourtreehill, and hospital, Foresthouse. Both are located far outside town indicating that Joy is not part of 'normal' society.
Joy is alienated as a woman, being unmarried and not fitting into any particular role.
Joy is alienated because of her depression and the stigma that surrounds it. It is a dirty secret that must be carefully kept from her employers.
Characters such as Mr Peach at the school also alienate Joy in their unsympathetic ignorant attitudes to her depression. Peach makes little effort to support Joy's true feelings. Instead he wants her to
smile and act as if everything is fine. And there is a lack of understanding of her eating disorder. It seems that both Ellen and Tony think she is too thin and this can simply be solved by feeding her.
Perhaps most significantly Joy is alienated because of her position as a lover rather than a wife. This is most apparent at the memorial service. The minister does not acknowledge Joy in his sermon, only extending sympathies to Michael's wife and family. Joy reflects that the Reverend Dogsbody has:
cleansed, absolved, got rid of the ground in stain. And the stain was me. I didn’t exist.
In this way, Joy is erased from the grieving process. Her social alienation in complete. As she perceives it, she has been literally blotted out of existence.
The miracle had wiped me out.
This revelation is an important turning point in Joy’s illness. It is linked to Joy’s eating disorder, by which means she literally diminishes and tries to get rid of herself.