Answer: Her doctor believed that intellectual effort was making her ill.
The passage was written during a time period in which women were encouraged to engage only in traditionally female activities. It was believed that women were mentally weaker than men, so their lives needed to provide comfort and safety, rather than stimulation. The doctor believed that intellectual activities (painting, writing, thinking, etc.) were making the patient sick, so he advised her to have a "domestic" life, stay home as much as possible and stop her intellectual activities.