She cries like an old woman because she is defeated and she is weakened and powerless to go back and change it.  She is defeated in the sense that the man from the repair wagon manipulated her and she read into it erroneously, thinking that he actually related to her and even took an interest in what was important to her, almost flirtatiously, when in the end, all he wanted was a sale.  In a sense it confirms that her husband is not the only man she has trouble understanding, and that the differences between men and women are universal.  This realization makes her feel more alone than ever way out on that farm with no one who understands her, like an old woman who has lived past her generation and who some may consider "obsolete."