What is an example of irony in the novel Ethan Frome?

An example of irony in Ethan Frome is Zeena valuing her pickle-dish too much to ever use it. Many people set out their most prized china only on special occasions. But Zeena declares that she "set most store by [it] . . . and wouldn't never use it, not even when the minister come to dinner or Aunt Martha Pierce come over from Bettsbridge" (chapter 7). She is saying, in effect, that she "sets too much store" by her pickle-dish to set it out for the kind of meal a treasured dish should be saved for. Her behavior could remind readers of the apostle Mark's question "Is a candle brought to be put under a bushel . . . and not to be set on a candlestick?" (Mark 4:21, King James Bible).
Since Zeena's pickle-dish, or "candle," was a wedding present, her real treasure may be her marriage. But whenever she is with Ethan, she either complains about her "ailments" or talks formally about mundane matters. She thereby locks her love inside her just as she hides her wedding present in the china-closet.
Zeena probably thinks that hiding her affection from Ethan keeps him from shattering it. But it is her cold, businesslike manner that makes another woman's warmth and cheer so attractive to him. For example, when Zeena is away, Mattie's eye-pleasing supper table fills him with a "sense of well-being" (chapter 6). He is probably delighted to see his favorite pickles in "a dish of gay red glass" (the pickle-dish) after Zeena had put the pickles in an empty medicine bottle.
In the scene in which Zeena discovers her pickle-dish is broken, there is a strong implication that Mattie is the "cat" that "got into the china-closet" and "chased a 'mouse' (Ethan) around all evening" (chapter 7). Her sobbing after telling Mattie "you've took from me the one I cared for most of all" suggests she has lost "one" she holds much dearer than a piece of china.
Zeena concludes that her prized wedding present has been destroyed because she has not preserved it well enough. But she has lost her true treasure, her joy in her marriage, because she has failed to show it. Her efforts to guard the light of her life under a bushel have allowed a rival to strike it out.