I must have missed this, but the character that Evangeline Lilly will play in the next Hobbit film is, well...
Completely. Made. Up.
Peter Jackson and whoever is helping him usher this project into existence just decided to add some characters and Tauriel (Lilly) is one of them.
If you had told me that this was what he was going to do, I wouldn't have been too surprised, but still. Just adding a character to such an established work takes guts.