This is one of the easier boss fights. I use Ruby and Xiao. As soon as the fight starts, run and hide behind a pillar at the far end. Jump out and attack her then jump back behind the pillar so that she doesn't freeze you (anti-freeze amulets don't work here). You'll hit her three times with a physical attack from Xiao then she'll throw up a shield. Rotate to Ruby and hit her with magic (I used fire, but it probably doesn't make a difference). The shield will fall, so you hit her with Xiao again. Whenever you get the message "no effect," switch to the other character. Rinse and repeat until she goes down.