So Cynthia knew the whole time! Yeah, this shouldn't be too much of a twist - Cynthia just went along with it because she wanted to make Helene have a Bad Time.
And FINALLY we get to my favorite part of the chapter, the punchline! This joke is very old - you can see here in a journal from 2015 where I sketched it out originally:
It's so rewarding to finally get to share a joke with my readers! I think it's a special kind of anticipation where you're about to share something you think is really funny but requires a whole lot of context for others to appreciate.