It's stated in the passage that Lady Margaret's illness ……………

The illness of Lady Margaret had long frustrated the skill and learning of her physicians. A settled resignation, a gradual wasting away of the body and frequent though short-lived attacks of schizophrenia were the unusual symptoms. Until now, she had fought bravely against the pressure of her disease and had not gone to bed. But on the evening of my arrival at the house, I glimpsed her climbing the stairs and noticed how pale she looked. Later I learned from her brother that she had given in to the power of the disease and that the few seconds I had seen her would be the last. The lady, while living, would remain in her room and be seen by me no more.