This has to be one of the worst parts of the game, finding Cauli Blackthorn. She is located in Murmorwoods as a statue (she was turned to stone) so you'll need a stone to flesh potion to free her. It seems that the stone to flesh spell will not work; so make sure you keep one of those potions you get when getting the quest. The problem is that you may only get three potions and there are six statues.
Ok so where is this woman? Well try the following location : X=15768, Y=14974. (you find the X,Y location by looking at the map for the area) This is the exact location that I found her, and I believe that she is in the same place for every game.
Problem: When you first meet Cauli look at the text choices you can make, one of them is to promote your Dark Elves. Make sure you do this at this time. It has been reported that if you don't do this when you first meet her, you won't get that chance again!