It is important to understand something of the context in which the story is based. Kate Chopin is an author who is famed for her presentation of women frustrated by their position in society. In the 1890s, the time when this story was written, women in the United States had little opportunity for self-improvement through education and employment, they could not vote and were not financially independent. We also know that Mrs. Sommers had enjoyed "better days" that her current penny-pinching state would suggest, but that her life was spent in constant battle to try and make ends meet so that she had no time for "morbid retrospection":
The needs of the present absorbed her every faculty. A vision of the future like some dim, gaunt monster sometimes appalled her, but luckily tomorrow never comes.
To this woman, then, whose every fibre is taken up with the challenge of making ends meet, a large sum of money comes. As she sits down, tired and exhausted, and runs her fingers through some silk stockings, which are said to "glide serpentlike through her fingers," the temptation to do something that she would never normally contemplate arises and she spends the money entirely on herself to give herself one day of pleasure and relaxation. Her desire at the end of the story that the cable car "would never stop anywhere, but go on and on with her forever," indicates the way in which she will struggle to return to her financially challenged life.