When are you dropping her? I know something similar happened to me once when I placed her too soon. The Pumpkin King had not yet been close enough to block, and once she was placed, he began attacking, slowing him enough for her to start fighting the smaller pumpkin instead while he slipped past, and Dracorich came out and began fighting her. I find it works best to place her when the Pumpkin King is halfway across the slot.