Final answer:
The Marquise de Saint - Meran likely believed she was nearing death due to symptoms similar to literary characters facing terminal conditions, as exemplified by Madeline Usher's mysterious illness and Georgiana's fatal birthmark in their respective stories.
Step-by-step explanation:
The Marquise de Saint - Meran most likely believed she was about to die because of the symptoms she was experiencing, which could indicate a perception of her own mortality due to a terminal condition or a grave illness. Literary characters who sense their impending death often do so as a result of acute bodily sensations, dire medical prognoses, or an overall decline in health.
In the context of the passages provided, characters like Madeline Usher and Georgiana both exhibit symptoms and conditions that lead to this realization.
For instance, Madeline suffers from a mysterious illness with cataleptical symptoms, while Georgiana has the fatal birthmark that her husband Aylmer is obsessively attempting to remove. Similar to these characters, the Marquise de Saint - Meran might be experiencing a combination of physical ailment and emotional distress contributing to her foreboding sense of death.
The Marquise de Saint-Meran believed she was about to die due to her severe illness and worsening condition. In the text, it mentions that she had a gradual wasting away of the person, frequent transient affections, and a partially cataleptical character.
This combination of symptoms led her to believe that her illness was becoming increasingly debilitating and ultimately terminal.