Final answer:
Without text references to a character named Scout or a pageant, it's not possible to answer why she keeps her costume on post-pageant based on the provided texts.
Step-by-step explanation:
The student asks why Scout keeps her costume on after the pageant. This question pertains to a character in a novel, suggesting an analysis of the text to understand the character's motives or circumstances. In the provided references, there is no character named Scout or an event that directly resembles a pageant.
Therefore, it's impossible to provide an accurate and detailed explanation based on the provided text snippets. A student seeking an answer to this question would benefit from reading and analyzing the specific novel in which the character Scout appears, likely Harper Lee's 'To Kill a Mockingbird', where Scout wears a costume during a Halloween pageant.