Mother happens to be at Mrs. Luddington's farm when she comes down with yellow fever. Mrs. Luddington puts her to bed, but Mother is so worried about what has become of Mattie that she takes a horse and goes off to look for her. The Luddingtons find her a few days later on the side of the road. She is almost dead. They take her home and put her to bed. The Luddington's try to get a doctor for her, but none come out, probably because the epidemic is keeping them so busy. Therefore, Mother has to recover on her own. She does, but she is still very weak. She has to take naps, which had not been the case before.
When Mattie asks her if the doctor has prescribed a treatment, her mother says she is supposed to be a woman of leisure; in other words, not do very much.
It was probably lucky for Mother than she could not get a doctor. As the appendix notes, in those days, doctors like Benjamin Rush treated yellow fever patients by bleeding them, which weakened them, and by prescribing medications we know today to be poisonous, such as mercury. As the French doctors knew, rest, fresh air, and plenty of fluids are what yellow fever victims need, and that appears to be what Mother received as the Luddington's home cure.