Mr. Showbiz Interviews Liv Tyler - "Basically, there wasn't enough female presence in" LOTR
It's been expanded from the books. There's a big appendix at the end with a large chapter about Arwen. Basically, there wasn't enough female presence in a lot of the film, so they took the appendix and used that story and placed it throughout. We shot all three movies at once. It took a year and a half, back and forth to New Zealand.
Hmm. I don't remember the appendices describing Arwen being chased by the Black Riders or talking with Morwen at Helm's Deep. Anyway, please click on the link below to read the rest of the interview.