Central to understanding this excellent story is the way that Mrs. Sommers is described as a character who has formerly enjoyed better times but now has been used to poverty for a long period. Note how this is introduced in the first paragraph of the story:
Little Mrs. Sommers one day found herself the unexpected possessor of fifteen dollars. It seemed to her a very large amount of money, and the way in which it stuffed and bulged her worn old porte-monnaie gave her a feeling of importance such as she had not enjoyed for years.
Note the way that the money changes the way she feels about herself and also the details we are given about her purse, which is "worn" and "old." The way that money is of such importance to her is emphasised by the precise way in which she plans to use the money. She is absorbed in "speculation and calculation." She literally spends hours carefully considering how to best use it for her family. It is clear that she is a woman whose every energy is focussed on making it through each day. Although she had enjoyed "better days," now the needs of her faily take up all her time:
She herself indulged in no such morbid retrospection. She had no time--no second of time to devote to the past. 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.
Therefore we can say that Mrs. Sommers is a very brave woman, having enjoyed wealth but now having to make do with poorer circumstances. She however does not give in to despair but rises to the challenge and gives her all to coping with these circumstances. However, the exhaustion and the toil of such poverty tempts her into indulging herself with the money she has.