Marriage of convenience with oc hobbit
Fem oc hobbit is friends with Bilbo, but she is disliked by every other hobbit. They are in a relationship of convenience. There are no romantic feelings on either side, but she needs protection, and he needs to hide the fact that he's not interested in women. She is malnourished because Bilbo has plenty of food for one hobbit, but not quite for 2. She is friends with rangers, so as a result they taught her how to hunt. She is out hunting when the dwarves come to the smial. She comes back dressed as a man (for hunting purposes) and carrying a deer. This gives off the impression that she is a guy, along with the fact that as soon as she sees the dwarves she throws the deer at them and attacks. She goes on the adventure instead of Bilbo.
The trolls traumatize her because she believes killing them by turning them to stone makes her a murderer. And murderers are exiled from the shire because of the incident with Smeagol and Deagol, so she thinks she can't ever go back to the shire.
She collapses at Rivendell. At the healers, a couple of the dwarves find out she's female (Balin and Oin, I think). The elves inform them she's malnourished, and give the dwarves a brief overview of hobbit eating habbits, and the reasoning.
While in goblin town, she gets a concussion when she falls, and picks up the one ring, thinking it's her prop ring. She is unable to put up a proper defense (concussion), which is why she riddles with Smeagol, instead of fighting him. Several times she stops him from attacking her by telling him he's her friend. When Gollum demands the ring, she shows him the two rings and tells him it was an accident, and mixes up the rings when she gives one back to him.
I can't remember if it was completed or not, but it was either on ff.net or Ao3