Probably the strongest example of irony is one we learn as the book ends. Jeannette's mother Rosemary had considerable wealth that could have fed and clothed her children and provided a home for them, but she felt she needed to hold on to this property. This irony is foreshadowed by the children's discovery of a diamond ring. When they learn that it is a real diamond, they want to sell it, but Rosemary says that she "should have nice things."
The title The Glass Castle highlights the irony of the castle Jeannette's father Rex promises the children. Although he is knowledgeable scientifically, it becomes clear to us that the glass castle will never truly exist. It is ironic that he describes it as glass because glass is fragile and unsustainable, like the Walls family itself. It is also ironic in that it suggests a fairy tale existence in contrast to the squalor in which the family actually lives.
We can see irony in the loyalty and love the children have toward their parents despite what many of us would consider neglect and even abuse. It is this mix of love and dysfunction that makes this a conflicted and powerful book.
There is even irony in author Jeannette Walls' fear of what people would think of her after she published the book. In an interview she claims that she was fearful of people's reactions. This is ironic in light of the resiliency she shows in the book itself, but it also reflects the mix of vulnerability and resiliency (possibly an ironic mix) that drives the narrative of this book.