The movie script made up the "life of the Eldar" line. In the books, Arwen (like her ancestors) was half-Elvish, and so had to choose which race to be counted among. For some reason, she was allowed to postpone her decision until her father Elrond departed Middle-Earth. At that point she had to choose, and obviously chose mortality for Aragorn's sake.
There's some comment in one of the auxiliary books (maybe Unfinished Tales) about the bitterness of Arwen and Elrond's parting at the end of the 3rd Age. I think a more specific explanation of the issue is buried somewhere in Tolkien's Letters or the Histories of Middle-Earth.
Anyway, good on PJ
and company, 11 Oscars is quite a feat. And now to bed...
Keynes is dead and we are living in his long run.