Do you remember Holly's story
In Omne Tempus ? There was another writer that used the same facts for her story (it was the BSV challenge 106). Sadly there aren't the authors listed that wrote a story for this challenge. I think this other author wrote the fic that you're looking for. I didn't read it because I didn't like the Buffy/other.
I *think* that the author's name started with a W but I can't find the story here (yet I saw it posted here before). Maybe when you'll find the author again you'll find the other story.