While a young girl, Katrina stumbles upon a unicorn drinking from a
  clear pool.  She is delighted to discover that the creature permits
  her to touch it before it bounds away.  Laughing, Katrina gives
  chase, pursuing the unicorn through the elven wood.  Katrina's
  pursuit eventually leads the distracted unicorn into a disguised pit
  trap.  Katrina, arrives on the scene to find the goblins surrounding
  the pit with spears and a net.  Afraid for her own safety, Katrina
  remains out of site of the goblins, when a human wizard appears.

  Katrina watches, transfixed, while the human wizard orders the
  goblins to hold the unicorn.  The wizard reaches into the pit with a
  cruel blade and removes the unicorn's horn.  With the bloody horn
  still in hand, the wizard tells the goblins to ``Finish it off; it's
  worthless now.''.  The wizard then walks over to where Katrina is
  hiding in the forest, and says ``Thank you, my dear...  Without your
  help, I would never have been able to finish creating my new magical
  dagger..'', and gestures to the horn.  He then smiles contemptfully,
  and he and the goblins disappear.

  Katrina runs over to the dying unicorn, but before she can reach it,
  a figure interposes itself - a fierce-looking dryad.  ``It is too
  late for you to help now; your actions have caused his death!''.
  Overwhelmed, Katrina professes her guilt, and begs the dryad to tell
  her some way that she can `make it up'.  

  In exchange, the dryad casts a curse on Katrina, such that no
  magical weapons or armor will function for her until she manages to
  return a horn to the unicorn.  Katrina agrees, and once a year, she
  returns to the elven wood, searching for the grove.  Every year, she
  sees the dryad and the hornless unicorn from afar, but every year,
  she does not have the horn, and so when she tries to approach the
  dryad and the unicorn, they fade from sight before she can reach
  them.

  Over the years, Katrina has kept up the search, but has come to
  accept the curse for its unusual positive side effect -- she is now,
  in some ways, ideally suited for search and retrieve missions
  involving magical weapons and armor that are believed to be cursed,
  since the curse will have no effect on her.

     Katrina would have the `limited magical item use' restriction,
     causing magical weapons and armor to not function (including
     curses).  This restriction is normally `5+' points, but it's
     silent about curses.  I'd go with it just for background sake.