Here's the big difference between those episodes: "Lice Capades" uses the lice as a weird/funny diversion from the real plot of the episode, which is actually about the kids and how they're little assholes. (Weirdly enough, that episode also has Cartman leading a crazy/hateful witch hunt, which kind of works and is…

To be fair when she started writing HP fanfiction it was around 2000, so she was more like a 27-year-old woman.