What deck you used? I used huge LIGHT monsters boosted by field spell and equip spell to farm her, so the condition for Cubic Mandala is never fulfilled, as she doesn't have a monster strong enough to destroy mine.
A BEWD deck. She only used it once after she destroyed my white stone of ancients so it's effect wouldn't activate. I waan't farming her though i managed to get the remainder of the cards and finish the event within a day or two before it ended