In Misfit in Middle Earth (2009), a linguistics graduate student named Barbarella (her mother is highly fannish) finds herself magically transported into The Lord of the Rings, more specifically plopped down onto the fields of Rohan some ways into the events of the first part of The Two Towers. She’s never read Tolkien and she’s seen only the first movie, so she has only a sketchy idea what’s going on, but -- to her own surprise -- she knows the languages of Middle Earth. Pretending to be a traveler from a distant land, and obviously of high estate given her smooth hands, she manages to get a job as Princess Éowyn’s handmaiden.
As the story progresses she takes a moderately significant role in the developments, but this isn’t Chicks in Chain Mail; she’s heroic, but believably so, for example organizing a field hospital for the wounded during the climactic battle rather than charging in with a broadsword.
In the sequel, Misfit in Minas Tirith (2010), Barbarella accompanies Princess Éowyn to Minas Tirith and again becomes centrally involved in the story without drastically altering Tolkien’s plot. She meets a number of original characters, including a very memorable elf, and it’s finally explained, or at least hinted at, how and why Barbarella came to Middle Earth.
From the title of the first novel I was rather expecting it to be comic, but the story is straight fantasy adventure, though Barbarella has a nice sense of humor and her first-person narration contains a fair amount of wit. I confess I haven't read much in the way of fan fiction, but I very much enjoyed both novels, in fact staying up almost all of one night reading the second one. As is typical with fan fiction, they can be read for free on line: