The easiest way I'm aware of, is to disable her from attacking, Kyia style. Last time I did it was with a mage. After I stepped down the ladder, I drew the dwarves as far away from J. as possible, then immediately drank an invisibility potion and ran to the back of the room (where she is), placed myself in a corner, then cursed her several times and then immediately froze her. This should be easy to do, because while you're casting Curse on her, she can't move or attack. Then just attack her till she dies (I used Elemental Arrows), or take care of the dwarves first if they're giving you problems (and then curse/freeze her again and kill her). Obviously you need the Curse and Freeze skills for this (or Polymorph instead of Freeze).
I'm not sure what her spirit resistance is though, so Curse level 1 might not work (because although consecutive casts of it stack together, the duration of each cast is still in effect and it may be too short at level 1 for all the casts to stack long enough to get her resistance below the level required by Freeze or Poly).
