At the surface she superficially spoils the lives of two vivacious characters in Brideshead Revisited, her flapperesque daughter and her puerile, dipsomaniacal son. They are unhappy figures who seemingly would enjoy their lives more thoroughly if not for the matriarch's religious rearing and burdensome oversight. Julia could freely marry Rex Mottram and his few developed faculties without the social stigma of a wedding in a divorcee chapel and Sebastian could dote upon his fellow aesthetes with as much Cointreau as his lubricated heart desired. The Catholic within screams "No, they have a God-sized hole and are filling it with frivolities. Their saintly mother knows better." The first statement is true, but the second does not necessarily follow.
Waugh sets up Anthony Blanche at the beginning of the novel as the seer of the story, as Tiresias, the clairvoyant prophet who dispassionately advises a wanderer. Blanche's disdain for the Marchioness dampens our impression during the few direct encounters with her in the novel. He paints a gruesome picture of Teresa Marchmain as manipulative with a compulsive victim complex, a woman who would make her husband appear to have eaten her children and danced about "wreathed in all the flowers of Sodom and Gomorrah."
Blanche, however, is not the only seer in the story. The younger daughter, Cordellia, is also a prophet, albeit a minor one when contrasted with Blanche. Blanche sees the characters in three dimensions and with five senses, often more clearly than they see themselves. Cordellia sees them through spiritual lenses. She recognizes Sebastian's spiritual struggle masked in drink, Rex's vapidity, Bridey's misplaced piety, and her mother's near sanctity; Teresa is nearly a saint, but not quite. She lost her brothers during the First World War and then her husband to an Italian dancer after it; she accepts loss, but does not deal well with it. While she is not unholy, she may be bitter, and it causes her to hew to her children until they find themselves constricted in a way they might not otherwise be. She could be a saint, but saints are detached and Lady Marchmain is not detached for fear of loss. In a cruel twist, her fear only ensures that she does lose her son, at least for her lifetime.
J interestingly compared Lady Marchmain and her unreasonable expectations to the Church and Her high standards for salvation. In fact, Lady Marchmain is not the Church in Brideshead Revisited, the house Brideshead is the Church, built atop sturdy old foundations and calling all who belong back to her. All the characters eventually return both to the Church and to the house, at least the ones who have left. Likewise, Lady Marchmain is not the cornerstone of the house, but she is one of the better bricks in it. Christ is the cornerstone.