The ironic mother
The mother in this novel is ironic in many regards, but of course the most obvious is that mothers have a natural attachment to their children, and even those with postpartum depression are aware of the wrongness of that emotion—with counseling, many women survive postpartum depression in stride, learning to love their children. This mother does not even do that. She not only does not love her child, she also actively exploits the child's weakness, manipulating the child by starving the child of love.
Childhood guilt
Ruby comes away from childhood upside-down and backwards. She must realize somehow where her self-hatred and hopelessness come from, or else she will eventually succumb to the destructive powers of her depression and agony. What she finds is a dramatic irony relating to her childhood guilt; the portrait of that guilt indoctrination is evident in the plot, but it is most evident in the end of the novel where Ruby reflects thematically on guilt. She decides that children are inherently innocent and that her mother is abusive. This clarity partially frees her from her mother's opinion.
Drama and repression
The dramatic irony of Pearl's death is invoked by a mother's boyfriend—one of many to be sure. That memory was repressed by Ruby because at that age, her brain decided she was not developed enough emotionally to handle the truth of her sister's death and her mother's betrayal. However, when the boyfriend spills the beans, he sets in motion an ironic effect; instead of manipulating her into more self-hatred, he reveals to her a piece of evidence about her mother so heinous that Ruby is finally about to forgive herself for her sister's death.
Pearl's surprising truth
Pearl's mother was actually responsible for the death of her daughter, and when Ruby learns this, there is dramatic irony through and through. Pearl and Ruby were instructed by a hateful mother to go and play on this ice. Ruby has to wonder why the mother would want to endanger her children. When only Pearl dies, she clips Ruby's wings by making her culpable for her sister's death. This mother is a child murderer; she takes life completely away from Pearl so she won't be so annoyed by the children, and she takes Ruby's emotional innocence away, crippling her through childhood.
Escape and rebirth
When Ruby walks away from her mother's dominion, she encounters the dramatic irony of her own self. She realizes that she has a choice about who to trust. Although naturally all children want to depend on their parents, Ruby realizes that she will have to establish a community of people who actually love her, but outside her mother's home, she realizes that such darkness does not define the human race. Most people are fairly decent she sees. Even Patricia has approval to offer Ruby, though it is another emotionally challenging relationship for Ruby.
