A few musings... Do we know if Justine has any magical capability of her own, or is that even needed as long as you perform the proper ritual for summoning outsiders (like following a recipe), given that these are things that WANT to enter our world, whereas other beings might object to being summoned? Or could it be that she is a willing host for the walker, and the walker then temporarily granted her the magical spark, in the same scence that the fallen angels in one of the denarian coins can lend you powers temporarily, and they act through you?