I found that what was easiest for me was to place my self against the floor.
Two options, easy one first
1.) Blast her while shes bouncing around the room, if you're hanging on the floor or swimming close enough, she cant hit you. When she switches back into her alcove to launch her missile barrage at you, switch to Nadjia and use the shield spell. Most blasts will miss you and the few that do, reflect off.
2.) There is a perfection position on the floor, as mentioned above, that her missiles actually can't hit you due to the arc they have to make. Attach there and blast away in energy mode.
Either way, its a fairly long battle since most of your shots miss her when she's floating around, but if you beef up on Volcano rolls, or spicy rolls, she won't take long at all.
