How does the author use irony in the novel, Washington Square?

One example of irony can be found in Dr. Sloper's continued insistance that Catherine promise she will not marry her former beau upon his death. Her refusal to do so causes Dr. Sloper to cut her inheritance to a fifth of what it once was. In the end, Dr. Sloper dies believing that his daughter is still in love with her beau. Therefore it is ironic when Catherine refuses even friendship with this ex-fiancé.