I personally died only once to her. I faced her like it was pvp. When she casted spells, I interupted, stunned etc. If I had none I would force speed to the closest pillar so her cast couldnt finish. I would taunt off of khem when he was nearly dead. Although the second time I faced her khem bugged and died when she was at 70 or so %. So its easily doable without him. Just play it like its pvp and abuse her. Interupt her at all costs! Or just pillar abuse. I did this as an assassin btw.

I did this today at level 20 and with Kehm. I popped the use the force skill (forgot the name gives a min long of 2% hp). When adds spawned I killed them instantly while Kehm tanked. Just go behind, maul a lot, and that was pretty much it for me, Kehm died at the very end but I did it. I used surging charge as my stance thing. I am deception.