I would imagine it's the mind...... the mind is a powerful thing ---
Placebos were a huge success years ago, and sometimes still today --- as if you tell the patient you're giving them ibprofuen, but it's really just a pill of sugar... and it still works.....
Same thing with illnesses and sicknesses.... If you keep telling yourself you seem sick, you're mind will create the symptom - my uncle taught us that when were very little, not to worry ABOUT HAVING SOMETHING, because your composition can play tricks on you.
So in her case, the moment she heard COVID, she knew the symptoms, and it's like a bad shot in the arm.