Why was the woman who entered the carriage upset?

According to her husband, the woman is upset because their son, an only child to whom they have “devoted their entire lives” is set to leave for the warfront in three days time.
The couple enters the “stuffy and smoky second-class carriage” that already has five people in it, in the early morning. The two appear melancholy: The text describes the woman as “bulky and in deep mourning,” and the man as “puffing and moaning” with a “death-white face.” When the man asks his wife whether she is fine, she does not answer and instead “pulls her collar to her eyes, to hide her face.” The man then feels it in order to explain to the rest of the travelers in the carriage what the matter is with his wife. As he does this, the woman “twists and wriggles, sometimes growling like a wild animal,” for she is sure that her predicament isn’t to be pitied as there must be many people going through similar, if not worse experiences as a result of the war. Indeed, after her husband’s explanation, some of the travelers venture to explain how they too have suffered because of the war. One says that

“You should thank God that your son is only leaving now for the front. Mine has been sent there the first day of the war.”

Another says,

“I have two sons and three nephews at the front.”

They argue that they all are suffering from having their sons at the war-front and that the couple’s suffering isn’t unique.
One of the travelers, a fat old man with “bloodshot watery eyes of the palest gray,” joins the discussion and says that perhaps, it is better for their sons to die young, “without experiencing the ugly sides of life, the boredom of it, the pettiness.” He says that he does not cry even though he has lost a son at the war-front, for, before his death, his son sent to him a message saying that “he was dying satisfied at having ended his life in the best way he could have wished.”