I can't say anything about Valerie.
What I read is that Gasper has a good opinion of her. What I don't know is: if she has a boyfriend/husband or are there any other circumstances. So it is purely speculation. I agree with your point that it is very likely that there will be a vampire in Ise's harem, but who?
Secondly the point about the writer making it in Ise's favor? I doubt it because he has said already, before he will introduce new characters into the harem. He will first give the last 4 (I believe) more attention. Second reason why I don't think Valerie will be in the harem she can't! She leads one of the vampire factions. How could she move from far far away ( or were ever) to Ise's house and become part of his Harem. Local wive is possible but I don't think it will happen because it is just impractical.