I've always found this fight easy. Have all four characters in position around the room sneaking, make sure doors are closed, and take her down in a surprise round (or if your initiative rolls good enough you may have 2 rounds before she calls for help).
Nobody ever heard her screams.... >:D
Also on the remark of the AI companions getting the mark. They can, you just need to select that character and initiate the conversation with them. I've generally got it on my whole party, as there's no negative to doing so in EA.
