[Pirengle]

Switch on the Inner Sanctum (ethereal) mode in the Battle Squares room. I think it's the far right switch. When Oria breaks her staff of power, it turns her ethereal. By throwing the switch, your party enters ethereal mode and can kill her.

She's hard to find. Try moving your party to the Battle Squares room to throw the switch then haste a party member to go search for Oria. Sometimes she shows up at the Battle Squares room once you've activated Inner Sanctum mode. Other times she's hanging out in odd places, like the stairs to the level or the coffin room. (Don't worry--she'll be somewhere on level 2.)