That would be spoiling the fun, though, wouldn't it? I mean, just because my SO is playing the follower of a demon lord with numerous family issues doesn't that her sister has issues! She was (until her untimely death) just your every day elven royalty. And just because her story starts "like so many of my friends, my story starts when I died..."
All that being said, Savage Species has guidelines for playing monsters, leveling them up as you go until, at some level, they are a fully developed something. In this case, she would be a 7th level succubus...er...elf bard! Elf bard! I meant to say elf bard!!!