This is a great question. Chopin cleverly does not explicitly state what the past life of Mrs. Sommers was like but we are left with enough clues and hints to infer that in her past she had enjoyed much more material wealth than she does at present. Firstly we have in the initial paragraph the sense of "importance" that carrying around a large amount of money gives her, "such as she had not enjoyed for years." Then we are given other tantalising glimpses of her former life from the narrator, who tells us what the neighbours think of her before giving us the view of Mrs. Sommers herself on her lot in life:
The neighbours sometimes talked of certain "better days" that little Mrs. Sommers had known before she had ever thought of being Mrs. Sommers. She herself indulged in no such morbid retrospection. She had not 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.
Note how this description emphasises the sad state of affairs that Mrs. Sommers faces now. She literally has no time to dwell on past circumstances, or to focus on the terrifying vision of the future that is compared to a "dim, gaunt monster." Survival of today takes up her every waking moment, giving her no time to dream or worry.
Lastly, we are given another hint as to her past circumstances when Mrs. Sommers buys two magazines:
Mrs. Sommers bought two high-priced magazines such as she had been accustomed to read in the days when she had been accustomed to other pleasant things.
Thus we can infer that either Mrs. Sommers came from a family that had money but made a disadvantageous marriage, or that she and her husband once had money before suffering some kind of economic collapse. Either way, understanding her past makes appreciating her desire to have a day of luxury once again more comprehensible.