Star Wars: Knight Errant by John Jackson Miller
A lone Jedi in Sith space dedicates her life to bringing down Sith rule, one act of sabotage at a time. A thousand years before Star Wars: A New Hope, the Republic is in a dark age and groups of Sith have taken over vast swaths of the galaxy. Hiding in one Sith hell-hole is Kerra Holt, a young Jedi working alone to destroy the Sith Masters. But what she doesn't know is that she just might be the pawn of a powerful Sith Lord...