Final answer:
Evelyn's focus on the ketchup stain on her outfit even after it has been removed is an example of centration, a characteristic of preoperational thought in which a child focuses on one aspect and ignores others.
Step-by-step explanation:
The behavior Evelyn is demonstrating by insisting that her outfit is ruined even though the ketchup stain has been removed is an example of the preoperational thought characteristic known as centration. Centration is the tendency to focus on one salient aspect of a situation and neglect other, possibly relevant aspects. In this case, Evelyn is unable to appreciate that her outfit is not ruined because she is wholly focused on the incident of the ketchup stain, even after its removal, and therefore unable to consider the bigger picture that her outfit remains clean.