A random thought or two occurred to me...
First the more normal approach here, what if our poor and delicate teacher was "taken ill", so could not continue helping to just count all of the children, so suddenly ended up with more spare days and spare time to return to the museum...
The more unlikely, but wickedly appealing thought, perhaps some rule gets broken, she is arrested, and ends up back at the museum, due to some strange technicality, while they wait to sort out her situation, and the school trip carries on without her...
Either way, I think we all really want to see more of this story, and the sooner the better [
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