The Lord Of The Rings: What Happened To Elrond's Wife
While she isn't in the main narrative of "The Lord of the Rings," Elrond's wife, Celebrían, is an important part of his backstory, and her absence is actually a key detail of the larger "Lord of the Rings" story. The Elven lady of Rivendell's MIA status doesn't mean she's dead, though. By the time of "The Lord of the Rings," Celebrían has left Middle-earth for Valinor and the Blessed Realm over the sea to the west of the Middle-earth continent. But if you want to understand why Elrond's wife (who is also Arwen's mom and Galadriel's daughter) is absent while the rest of her family is still traipsing around Middle-earth resisting the Dark Lord Sauron, you need to back up a bit.
Celebrían is the daughter of Celeborn and Galariel. (Yes, she's part of that Galadriel's family tree.) She was born at an unknown point during the Second Age. But we know she's old enough to notice the hunk Elrond when her family visits the newly created Elven fortress of Rivendell. They hang out there for a while, and the book "Unfinished Tales" adds the line, "and it was then that Elrond first saw Celebrían, and loved her, though he said nothing of it." Fast forward several centuries to the early Third Age (the three-thousand-year-long age that ends with the "Lord of the Rings" story), and the immortal lovebirds get hitched. Soon after, they have twin sons named Elrond and Elros, and then Arwen follows.
Celebrían was attacked by servants of Sauron
The only hint we get of Celebrían's fate in the actual "Lord of the Rings" books is a mention in "The Fellowship of the Ring." When Frodo Baggins arrives at Rivendell and sees Arwen for the first time, the description of the daughter of Elrond is followed by this line: " Her brothers, Elladan and Elrohir, were out upon errantry; for they rode often far afield with the Rangers of the North, forgetting never their mother's torment in the dens of the orcs." This chilling reference comes up again in the appendices that J.R.R. Tolkien included at the end of "The Return of the King."
There, we get a slightly longer explanation when it says that in the year 2509, 500 years before Frodo's quest, Elrond's wife "was journeying to Lórien when she was waylaid in the Redhorn Pass, and her escort being scattered by the sudden assault of the Orcs, she was seized and carried off."
Once captured, the gentle Celebrían is tormented in the Orc dungeons and is even given a poisoned wound. Eventually, her twin sons, Elladan and Elrohir, discover her and carry out a rescue mission. They bring her back to Rivendell, where Elrond uses his healing skills to repair her physical body. However, the book adds:
Though healed in body by Elrond, [she] lost all delight in Middle-earth, and the next year went to the Havens and passed over Sea.
We don't know what happens to Celebrían after she leaves Middle-earth. But it's safe to assume that she gets at least some kind of rest. This is because she is headed for a continent over the seas called Aman or the "Undying Lands."
Celebrían found healing in the West
The continent of Aman includes the region of Valinor or the Blessed Realm. This is a hidden realm maintained by the angelic guardians of Middle-earth called the Valar. These spiritual beings in incarnate bodies share their home in Valinor with the immortal Elves who choose to come live in that hallowed land rather than remain in Middle-earth.
While tragic, Celebrían's early departure into the West isn't some kind of ending or failure. It's a move clearly made in search of healing. It's safe to assume that the mentally and spiritually broken Elf likely finds at least some kind of rehabilitation in the Blessed Realm. After all, that's why other Elves like her husband, father, and mother eventually follow her after the War of the Ring. It's also the motivation behind the special permission given to a handful of mortals to go West and leave Middle-earth (including Frodo and Bilbo Baggins).
While J.R.R. Tolkien never confirmed this, it's completely reasonable to hope that Celebrían ultimately reconnected to Elrond, Galadriel, and Celeborn. As far as her kids, though? We know Arwen's tragic ending at the end of "The Lord of the Rings" for sure. She never gets out of Middle-earth. But her brothers? The last note we get about them is in the prologue to "The Fellowship of the Ring," where it says that after the "Lord of the Rings," "[In Rivendell], though Elrond had departed, his sons long remained, together with some of the High-elven folk." Celeborn joins them for a while after Galadriel goes West, and it's confirmed that he eventually leaves to follow his wife. As for the twin boys? They probably go with their dad or soon after him. But we never got any more details about them.