At the beginning of the story, Rosaura is looking forward to going to her friend's birthday party. Rosaura's mother, however, does not want Rosaura to go to the party. Rosaura's mother says that the daughter's friend is not really her friend and that the daughter's friend has only invited her because she, Rosaura, is "the maid's daughter." This is where we learn that Rosaura's mother makes a living as a maid.
Rosaura's mother appears to be a maid for a very rich family. She says that she doesn't want her daughter to go to the party because it is "a rich people's party." During the course of her employment as a maid, Rosaura's mother seems to have arrived at a very negative opinion about her employers. She seems to think that the family are "liars." She also thinks that they have invited Rosaura to the party not as a friend but as a maid, to deputize in her mother's place.
Later, at the end of the birthday party, Rosaura unfortunately discovers that her mother was right after all. Rosaura's supposed friend gives all of the other children at the party a leaving gift, but to Rosaura, she gives only money, as payment for her help during the birthday party. At this moment, Rosaura realizes that she was indeed invited to the birthday party to be a maid, just like her mother.