Why not Ollie? I read this story once, I forget the girl's real name, but her nickname was Ollie. Her real name was related to the name Ollie, but I forget what it was XD
I thought of that, but the name Olive doesn't fit the image of her. And, being picky here i know... I don't really like the name Olivia... >.> I thought of making her "real" name Olive or Olivia and then Oliver being a nickname since she's kind of a tomboyish character... But, I'm not fully sure about it. Oliver is just the name that got stuck in my head.