The author just showed how well some people can dumbass the innocent. The expression, which is also a colorful one "Tom Sawered" clearly explains how Sadie convinced both Julia and Penny into doing her boring work.
" “I think we just got Tom Sawyered.”"
The two girls are do not love the work either. However, parties cannot happen without hard work. Who does it? Obviously, the less worldly, who can get tricked into doing others' job.
Dialog and the main point come through very well.

An amusing story.

Write on!