Wheels revolve around axles but it's the wheel that catches the eye not the axle - your posting read a little like that to me, that it'd all be based around her but (unless mainly told in flashback format) by being read by another is open to interpretation and experience by another.
As a reader I have problems with flashbacks - jumping back and forth in time breaks the story up for me and I can get bored of working out where I am and pick up a different book (or film) instead, diary formats can be predictable and uncomfortable too.
If your Succubus is going on a voyage of discovery perhaps have her find the old memoir and work on from there - if she's going to be a decendent of the hyperboreans this could work quite well, while someone finding her memoir centuries later isn't going to give a lot one way or the other.
Plus, are we centering this around Grecian mythology too much? I know we're only batting around ideas at the moment as we've no group consensus till after monday when Matsamu closes the admittance, but I thought we were playing God and creating our own world/s rather than adapting the existing one?
It's a concept that could carry well into a 'new world' though - along with a lot of the other mythology we've been chatting over
