As a level 50 spirit cabalist, I died five separate times fighting Deliah. I recommend major caution if you are used to letting your simulacrum do your fighting, as the simulacrum will get lost when she begins teleports.
The fight is actually really straightforward.
First you must get close to her.
BUT DO NOT GET TOO CLOSE! She will melee staff you.
Now if you are in the correct position, then either Body debuff her first or go straight to draining her essence.
May the light of Camelot shine on you. I /use Hope you succeed.