Choose the best reason du Maurier includes Nat's comment to his wife, "We'd be better off in the old days," in her short story, "The Birds."
In Daphne Du Maurier's short story, "The Birds," Nat's comment seems to point to the first answer, "Nat's comment foreshadows coming events."
"We'd be better off in the old days . . . . when the women baked twice a week, and had pilchards salted, and there was food for a family to last a siege, if need be."
I believe this is foreshadowing. This is not a comment that refers in any way to a "woman's place" within the home. Nat's wife will not be predicting what is going to take place, as Nat is the observant one who is concerned about the birds when no one else sees the threat. And this is not how an author, generally, presents the setting to the reader. There is usually description of the location or a mood, not conversations such as this one...in general.
Knowing how the plot unfolds the story, one can understand how this would be foreshadowing. The first night, the birds attack ferociously; Nat eventually has to go out to get provisions (though because the birds are "full," they don't bother him). He travels to the Triggs' farm to do so, and finds the Triggs, and Jim (the hired hand) dead.
At first, Nat's comment is spoken with the idea of how much easier he believes life was in "the old days" by not having to run out for provisions as they do now. After the bird attack, his comment is more meaningful: he is fearful to go out, but must. If they were living as people did in the past, they would not have to face the deadly birds because they would not have to leave the house for supplies.