The irony of British loyalism
The conflict between the Irish and the British is long-standing, but it's still ironic when suddenly, a real war breaks out, and suddenly Captain Gault is in the crossfire—the Catholics don't accept him for his Protestantism and Loyalism, but the British don't like Irish people. Captain Gault is rejected by every party.
The irony of miscommunication
To avoid tactlessly hurting their daughter, these parents choose to keep Lucy in the dark. That comes to bite them though, because Lucy misunderstands the severity of the situation and makes a choice that she wouldn't have if they'd tried to talk through things with her. Then, her parents misunderstand the situation too, thinking she has died. These are three instances of the same ironic problem—no one is talking through things.
Lucy's "getting what she wants"
Lucy experiences a great deal of shame in her life, primarily as a response to the silly notion that perhaps she is guilty for everything that happened, because she decided to hide, thus "Getting what she wanted." This is ironic, though, because the real reason her parents left was the political strife of Ireland. Lucy wrongly associates them leaving with her fighting to stay and then insisting. The irony is redoubled because Lucy feels the universe is punishing her with "what she wanted" just to teach her a cruel lesson about loneliness.
The ironic depiction of mental health
Almost everyone in this story is mentally disturbed. Lucy realizes that she cannot connect with others emotionally, because her entire emotional faculty is constantly trying to work through the trauma of her abandonment. Then, she meets her dad, trying to find peace, and she finds that he is in the same boat she is in, aloof, mentally unwell.
Finally Lucy finds catharsis in her friendship to the boy her father shot, as if seeing the physical wounds helps her to understand her trauma better. Like the boy, she was wounded and became ill, but it happened in invisible ways, so her body is confused about it. Visiting the boy in the asylum helps her see this, which is ironic, because it reverses the role of the crazy boy.
The irony of technology
The novel ends cleverly with a nod to the introduction of the internet age, something that Lucy understands only a little about. She is constantly perplexed by technology. Technology represents the forward progress of man, since time brings new innovation, so technology is like a reminder that the earth keeps on spinning, and somehow, that seems discordant with Lucy's deep emotional and spiritual suffering.
Therefore the use of technology in the book is ironic, both because Lucy never could have expected the technological advancements that really happened, but also because technology is being used as a death reminder for Lucy, showing her that the passage of time is very real.
