Questions on Arwen (mainly): How should I explain it?

[The Only Real Estel]

I've got a question for you guys:

Whenever I watch TTT & RotK with someone who (a) hasn't seen them before or (b) doesn't have the clearest understanding of them I invariably will get a question about Arwen posed to me. Here are the two main questions I get asked:

#1-(TTT)- "Why does Elrond say that after Aragorn dies she will have to linger on in the world until 'all the world is changed'? Didn't she give up her immortal life in FotR?"

To which I usually respond by trying to explain what I thought PJ ment by it (which really isn't the clearest), in this case maybe that she gave up her 'guarenteed immortality' by saying that she wouldn't take one of the ships, but she didn't actually give up her 'conditional immortality'.
I've always been a bit iffy on this situation by the books (I'm starting to read up on it again), but I mainly made up that explanation based on the movies. Can you guys think of a better/clearer way to explain it?

#2-(RotK)- "Why is Arwen's fate bound to the Ring? I mean, everyone's fate is bound to the Ring, but Elrond seems to be meaning more by his comment than that."

How should I explain that?

Also:

TTT (Elrond)- "Why does Elrond stay behind at Rivendell & not take 'the last ship'?"

I usually answer that by saying that he stayed to look after the house, but mostly because all of the higher-up Elves (Celeborn, Galadriel, Elrond, etc.) decided to stay in Middle Earth until the conflict is resolved, even if they wouldn't play a part in it.

I'm not even sure that last explanation makes a lot of sense to me, so could you guys give me any other ideas?

Any help you can give me on any question would be great, just keep in mind that it's usually someone with very limited book knowledge that asks these questions, so the answers can't be to in-depth...

[Elianna]

Q1: Technically, she gave up her immortality 38 yrs ago (when she excepted Aragorn's proposal), and is only now going through with her plan. I think why Elrond says "until the changing of the world" is Fran, Phillipa, and Peter trying to fit in the lovely line in Appen A:

...And there is her green grave, until the world is changed, and all the days of her life are utterly forgotten by men that come after...

Q2: Because Jackson wanted to add more tension. That's the only reason. And the only explaination! Curse him!

Q3: They exaggerated that it was the "last ship" of course. And I think you're explaination works well. But throw in something about Vilya and the other of the Three and you'll confuse them enough that they'll stop asking questions whose answers lie somewhere in Jackson's fuzzy head...

P.S. love the movies at all, but I'm a purist.

[Gorwingel]

Many of the quotes that you speak of are ones that many fans have had the most problems with.

I guess you could tell your friends that every film adaptation has changes, and these are some examples of that (this would be bascially stepping around the problem). Then you could go on to tell an abbreviated version of the true Arwen story, or tell your friends to go out and get the book so they can figure it out for themselves (but then they would still be confused).

Basically the story of Arwen that I have determined and read is that she has no immortality, no choice no more, she's mortal. The quote from the film though I think refers to the time that she will have to go through after Aragorn has died, and when she will be all alone. But they wanted to make it sound more dramatic than something like "she will wander around till she dies" (which is basically what happens to her).

The other is just a troubled quote with no explaination. It's like the whole Faramir being mean thing