--"Unfortunately I borrowed my copy from Lavender, otherwise I'd show it to you."-- Shouldn't that be "I loaned my copy to Lavender"?
I must say I'm curious about the photograph myself. Despite the odd premise, this story continues to impress and entertain me.
Author's response
I think I see the confusion - if you look two lines earlier:
Parvati nodded eagerly. "Yes, I read a lot of Voyages with Vampires. It wasn't really a textbook though, more like a travelogue. You know, filled with his exciting adventures."
THAT is the book she borrowed, but no longer has (returned it, I'd imagine), so she can't show it to Harry.