This post is in response to gennastar, who reviewed chapter 7 and seems to be a little confused about Selene's roll in the story. In your reviewed you mentioned that Selene did not bring anything captivating to the story and asked me what made her useful.
While I understand where you are coming from, I think the reason you're so confused about Selene's roll is because you're not looking at the big picture. You're right, as of right now, Selene does not have much of a roll. In fact, after chapter 8, you won't see her again in this story. Her purpose here was only two fold.
First, I needed to introduce her character sometime before the end of Harry's 3rd year, where her purpose starts to become more important. Because of my plans for his 2nd year at Hogwarts and the summer before his 3rd year, the only feasible time I have to introduce Selene is the summer in between his 1st and 2nd year when he is studying under Nicolas Flamel. There was simply no other point in my story where I actually could introduce her.
The second reason is because vampires will have a strong roll to play in my story. In JK Rowlings books, she only ever mentions vampires in passing, and I think there was one vampire at Slughorns party in The Half Blood Prince, and yet Werewolves play a much more important roll in the story. It's like Rowling wanted to say 'yeah, vampires exist, but I don't want to go into details about them so I'm just not going to add them to my story' and left it at that. I want to actually give vampires, as well as a number of other magical creatures, a much more significant roll than what Rowling gave them. There is so much potential for these various magical creatures to play an important part in the Harry Potter universe, and I always felt it was a shame that Rowling never expanded on the various magical creatures like Vampires, Werewolves, Veela, Centaurs, Mermaids and other magical species.