So once she was able to slip away from dear old dad (nuncle) she played it to the hilt just as did Arwen's forebearer Luthien. Just a thought, don'cha know?
Bad comparison. Why would Arwen need to slip away ? L˙thien slipped away from dad because of Beren. Arwen didn't need to slip away : when she first met Aragorn, she was already 2710 years old. And when they got betrothed, Elrond didn't send Aragorn on a suicide-mission to get rid of Aragorn, but he accepted it. Also note that Arwen spent most of her time in Lothlorien, in her mother's land, until she met Aragorn (after which she returned to Lothlorien again). Only back in 3009 Elrond sent message to Arwen to return to him so they could spend their last days together. So Lothlorien seems to be Arwen's home, rather than Rivendell. And Elrond playing the dominant, over-possessive dad like in the movies, is a no-no.
Arwen loved her father dearly; she knew that their parting would cause him a lot of grief : that to me is the main reason why she would never leave Rivendell in the last days of the third age. Not because she can't help or doesn't want to help Aragorn : she does help him, but from a distance - remember she made and sent him the Banner.
Also, don't forget what happened to CelebrÝan in 2510 when she left Rivendell : that to me is a big reason why Elrond would never risk his daughter leaving Rivendell. And because Arwen loved her father dearly, she would never want to hurt him by leaving Rivendell against his will. The idea alone, is ridiculous. Arwen is an Elf who's nearly 3000 years old, considered wise. She's not ╔owyn.
Furthermore, again, Aragorn needed to prove himself worthy, not only to wed Arwen, but also to become a King. Arwen wouldn't help him actively in his "quest", she'd only support him by giving advice.
And again, this is true for book-Arwen. Who cares about movie-Arwen. Pah.