[Lalaith]

I really don't think it's as clear-cut regarding Arwen being half-elven, as some of you maintain.
At the first meeting of Aragorn and Arwen, Aragorn calls her Luthien Tinuviel, and Arwen says "I am not Luthien, but perhaps my fate may be like hers" (or something to that effect.)
In other words, up until the time she saw Aragorn, she had assumed her fate was that of the Firstborn.