Kiss of Death spell was patched to remove Certain Death and Limited Health slots around Aug 20th, 2013.
Killed her today and she cast Kiss of Death 3 times on 3 different targets. Each time the target was feign death and their hit points dropped to near zero (almost like Limited Health effect was still present). Healer merc, one who got kissed, was set to efficient to avoid big heals. There were no deaths.
It's possible Certain Death doesn't trigger anymore.