The Oedipal narrative
One of the reasons it might not be such a bad thing for Judy to be without children is that she might actually be unfit to raise a child in her compromised emotional and mental state. Mrs. Rice is a good demonstration of what might have happened if Judy got what she wanted; without the right foundations and structures in place, Mrs. Rice spoiled her son so much that he rejected his adult independence and stayed permanently as a thorn in his mother's side. Mrs. Rice's relationship to her son is the archetypal story of Oedipus, the Greek king who accidentally married his own mother.
The archetypal spinster
Judy Hearne is a significant character because everyone knows her type (think crazy cat lady). Her reality is one of the most terrifying possibilities for people, especially for women because many women want to have children and cannot, so this is essentially a horror story about an archetypal Job-like character (the Biblical character Job, that is).
Judy is a lonely, unmarried woman approaching menopause who has always wanted a loving husband and a family. She's Irish and Catholic (meaning she belongs to a disenfranchised and oppressed people group). She's a woman in the mid 20th century (not exactly the height of the feminist cause). She is lonely, and to boot, she is an alcoholic, so she is constantly traumatized and humiliated by her drunken stupors. This novel is a horror story about depression.
The motif of communal sin
Pay attention to how many characters have similar problems. Judy and Madden and Mrs. Rice's boarders deal with chronic poverty and instability. They all have been programmed to treat each other as enemies through hypocritical moralism. They all have desperate emotional needs that prohibit their success. Not to mention the alcoholism in the community. These are all indications of systemic issues in the UK. Suffering this widespread must mean disenfranchisement in the government or in society. It's an indication of the disenfranchisement of the Irish.
The picture of corrupt religious institutions
Father Quigley is an archetypal picture of the antichrist. Instead of showing unconditional love, he rebukes the needy and judges the suffering Belfasters. This is a picture of Pharisee-ism or legalism which is a problem that only few people avoid in their lives. Most people understand exactly what the novel means by Father Quigley's character, making him something of an archetype.
The motif of mental health issues
Undoubtably, Judy is mentally unfit. Her preference for fantasy above reality means she is not well-adjusted, and that's not a criticism against her character so much as it is an indication of her situation. She is hopeless. She suffers from extreme depression and crippling loneliness, and she makes her money and social problems way worse by her unbridled alcoholism.
