In Ethan Frome what does that author suggest with Mrs. Hale's statement that she didn't know what Zeena would have done if she didn't have Ethan to look after her?
The statement you refer to comes at the beginning of this novel, and serves the purpose of giving us a description of the kind of man Ethan Frome is, but also indicates the kind of frustrations that he must suffer. Consider what Mrs. Hale says to him about his frustrations:
I don't know anybody round here's had more sickness than Zeena. I always tell Mr. Hale I don't know what she'd 'a' done if she hadn't 'a' had you to look after her; and I used to say the same thing 'bout your mother. You've had an awful mean time, Ethan Frome.
Mrs. Hale's sympathy for Ethan Frome indicates the hardships that being married to such a woman as Zeena must bring. The way that this seems to have dogged his entire marriage, and also before that, as his mother seems to have been ill too, clearly suggests that Ethan Frome has had his life shaped by the sickness of others and their dependence on him. Mrs. Hale's comment suggests that Zeena is completely dependent upon her husband, which must be a great burden for him. Remember that at this stage in the novel we have not actually met Zeena yet, so this quote is important in giving us information regarding the kind of situation that the narrator is going to see when he finally makes it to Ethan Frome's house.