The irony of the failed attempts
The toughest part of Erendira's conspiracy to murder her grandmother is the fact that they failed twice before they succeeded. That means that it was not a crime of passion, but a calculated murder, and ethically, the severity of the crime calls Erendira's innocence into question, standing ironically against the title's suggestion.
The irony of family betrayal
The idea of innocence is that a mind has not been corrupted by the evils of the world, that a person has not sinned greatly enough to bring calamity on themselves, but also that they have been sheltered from tragedy by parents who strive to protect them. Compare that standard to the character in the novel. Instead of protecting her granddaughter, the antagonist subjects her to the tragic fate of forced prostitution. The exact opposite of what was supposed to be happening is happening to Erendira.
The irony of experience and progress
In order for Erendira to take her own interests seriously, she has to commit an unspeakable act, willingly and knowingly. Her violence is not the passionate violence of a confused person, but rather, she calculates her vengeance, showing that truly her innocence is gone, not by her own evil, but by the evil of others. This experience, although undesirable, entitles her to her freedom.
The irony of matricide
The mother is the giver of life, and the grandmother is too, by the same principle. So the granddaughter's decision to kill the mother character is a meaningful image, not unlike Freud and Jung's idea of the death of the parent. The abuse makes this irony more potent, because the irony of child abuse precedes it.
The irony of Ulises's service
Just as Erendira does her grandmother's will during her childhood, she also uses a proxy for her own interests by asking Ulises to murder her grandmother. Ironically, this makes her similar to her grandmother. Just as the grandmother violated her own granddaughter by proxy through prostitution, the granddaughter appeals to a man to get what she wants too.
