OMG, you should dress up as Sylvia! Just get the black fabric and a scythe, and you (or your parents) can make a wraith outfit... or, if the whole undead thing doesn't float your boat, put on a pretty green dress and a wig, and make a daisy-chain for your headpiece. :)
For the piece de resistance, find some 80s metalhead with a hideous beard (or a male friend with a wig, a hideous beard, and a creepy laugh) to be your escort. LOL.
On a side-note, I'm totally dressing up as Mithraya for my friend's Halloween party this year... If you're up to making giant wings out of bristol board, you could totally pull it off. :D