You can find some more information about this photo in the following
interview (look for "Lange" once you get there).

Basically, John Szarkowski found out that the words "end of an era" was more of a personal observation by Lange for the widow in the photo (her husband is dead and it's the end of her life as she knew it) , and not a social observation. Then Szarkowski makes the comment about how malleable photos are, and how the makers frequently try to nail down the possible interpretations with titles, text etc.