Over the course of Ethan Frome, Mattie and Zeena are consistently set up as foils of each other. In terms of looks and personality, the two women couldn't be more different. While Zeena is old, pale, sickly, and angular in appearance, Mattie is depicted as young, tanned, healthy, and curvaceous. While Zeena leads a sedentary and housebound lifestyle, Mattie goes into town for dances and picnics. And while Zeena is highly critical of Ethan and holds power over him, Mattie is more traditionally feminine and fills a more appreciative and subservient role.

As a result of these differences, the reader can easily understand why Ethan prefers Mattie to Zeena. But over the course of the novel, Wharton draws attention to several eerie similarities between the two women. For example, both Zeena and Mattie play similar roles in Ethan's life. Zeena arrived at the Frome farmhouse when Ethan was nursing his sick mother, and he latched onto her presence because he desperately wanted companionship. Mattie, meanwhile, comes to Starkfield at a time when Ethan is chafing under the responsibility of caring for his sickly wife, and she too provides him with the companionship he craves.

Despite their obvious physical differences, Zeena and Mattie are also blood relatives, and they so share a few characteristics, which become more striking when Ethan sees them in similar positions and locations. In Chapter 4, for example, Mattie stands in the doorway of the farmhouse holding a lantern, just as Zeena had done the night before, and Ethan is overwhelmed with a sense of déjà vu:

So strange was the precision with which the incidents of the previous evening were repeating themselves that he half expected, when he heard the key turn, to see his wife before him on the threshold; but the door opened, and Mattie faced him.

She stood just as Zeena had stood, a lifted lamp in her hand, against the black background of the kitchen. She held the light at the same level, and it drew out with the same distinctness her slim young throat and the brown wrist no bigger than a child's.

And in Chapter 5, when Mattie sits in Zeena's chair, Ethan momentarily sees Zeena's face on Mattie's body:

As her young brown head detached itself against the patch-work cushion that habitually framed his wife's gaunt countenance, Ethan had a momentary shock. It was almost as if the other face, the face of the superseded woman, had obliterated that of the intruder.

These moments of similarity foreshadow the ending of the novel, when Mattie's accident leads her to become almost identical to Zeena in terms of physical appearance and personality. In the Epilogue, the Narrator describes the two women as looking and sounding the same, and Mrs. Hale confirms that Mattie's disposition has changed to match Zeena's. When the Narrator first hears a woman's voice in the Frome house, he initially cannot tell whether it is Zeena or Mattie who has spoken. He even uses the word "querulous" to describe the tone of Mattie's voice, a word that was used earlier in the novel to describe Zeena.

By first contrasting and then comparing Mattie and Zeena, Wharton implies that, despite their differences, they both suffer as a result of the social expectations that were imposed on women of their time period.