I'm always amazed when people manage to knock out novel-length fics for challenges like this. How lucky is your recipient! It's like someone wrote an eighth book to her specifications. :)
I think that the best thing about this fic is that because it WAS so long and so detailed, the evolution of Harry and Snape's relationship was actually believable. I think that someone could have easily written the basic premise of this fic in 5000 words, but it wouldn't have had any sense of credibility.