you need +2 weapons or better to injure her. i recomend useing archers, because you find a badass bow, and lots of +2 arrows in her dungeon before you get to her. summon LOTS of creatures, send them into the room, then walk in and initiate dialog. use mages and druids to hit her directly, no area effect until your creatures are dead. that should do it for you.
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Morgan Corbesant, Elven BladeSinger, Captain of the army of the Seldarine