What is ironic about Zeena’s ability to care for the injured Mattie and Ethan?

Zeena's transformation is an interesting and ambiguous development. Some have read it as showing that Zeena possessed untapped reserves of strength and compassion; however, this reading runs up against some significant counter-evidence. The first is the narrator's description of her: "She [Zeena] had pale opaque eyes which revealed nothing and reflected nothing" (91). Hardly the description of a saint. Zeena has hardened to fit her circumstances; Mrs. Hale says that Zeena is not the one who suffers most, because she no longer has time to suffer. Just as she was able to care for Frome's mother, she finds it in herself to care for Ethan and Mattie. But her care is not marked by compassion or tenderness; this is care that comes because there is no other choice. And given what Chapter 7 revealed about Zeena's character, her transformation can be read very darkly. She can now afford to care for Ethan and Mattie because she no longer needs to worry about losing Ethan. If her earlier hypochondria was a way of controlling Ethan, it is no longer necessary. He is lame and needs her; in a similar way, Mattie no longer poses any kind of threat. All is stable at the Frome farm; there is no longer any way for Zeena to lose control of the situation.