The epilogue does state that Elanor was given the red book (the in universe writing of the Lord of the Rings made by Bilbo, Frodo, and Sam) and she was a maid of honor to Arwen, and was named by Frodo. Colbert stated the story would adapt chapters from The Fellowship of the Ring such as the Barrow Downs and such stuff. So there’s at least a foundation in what Tolkien wrote.