I like the interactions between Willow and her Gastly most of all thus far in this story. The Gastly is quite cute in its behaviour and lively as well, although I feel you could have gone without stating it when it was introduced:
The fic premise does seem differently handled here (given it's an OT fic and all), so I am curious to see what you do with it down the track. Fics that give some more attention to the professor aren't too common to begin with and including the info in the email isn't a bad idea either, heh. Wonder what is in the egg?
A few mistakes, but nothing major really. Just watch out for those things. Good luck with the rest of your fic!