Mrs. Drover comes across as a rather anxious, nervous woman. That's not surprising given her unfortunate experiences of life, as well as the ravages of war. In some ways, she seems to have aged prematurely. She wears no make-up, entirely in keeping with her plain, unprepossessing demeanor. The sudden appearance of a figure from her past indicates that Mrs. Drover wasn't always like this, that she had a much fuller, more active life when she was younger. But Mrs. Drover wants to escape from her past, and yet her past won't let her. It's as if she no longer accepts her former self and wishes to move on.
Her current family life appears to have given her some measure of emotional security, the kind she once thought her long-dead lover would provide. The letter disturbs this—albeit tenuous—sense of security, making Mrs. Drover nervous about what this means for her life. Haunted by a tragic past, threatened by a dangerous present in war-time, and fearful of what the future may hold, it's no wonder that Mrs. Drover's so incredibly nervous about everything. Her troubled mind has simply nowhere left to turn.