I agree with Blackrose - Yxonomei caused me much heartache!
In the end I sent in my cleric using Sanctuary and after the dialogue raid the area for treasure. I then ran like hell casting area spells and closing the doors behind me! Eventually I had just her and a couple of dying minions!
The first mistake I made on the way to Yxonomei was using my cleric and Sanctuary to raid all the rooms and avoid having to fight all the minions on the way to her. What happens on the way back? Spoiler...
Well all of the doors open as she chases you and there are hundreds more to fight! I thought this was cool (after doing it the right way!) and will not make the same mistake twice...especially as I am playing in Heart of Fury mode!