Answer:
Her experience best illustrates the agitating effects of an obsession.
Step-by-step explanation:
An obsession refers to a series of intrusive, unwanted and irrational thoughts which tend to "plague" an individual's mind, often having his/her main focus. These tend to trigger uneasiness in the individual or even distressed.
In this case, Mrs. Swift's intrusive and irrational thought that her house is contaminated by germs is a clear example of an obsession which could even trigger compulsions, such as extreme hygiene.
This could develop into OCD or an Obsessive-Compulsive Disorder.