Truth of the matter, is the truth in the story is what Jim makes it. Your basic genetics don't change, so basically you are who you are. Life's experiences are another matter, and I don't think personality is understood very well. The latter is born out by the cloning of pets, in theory the genes are the same, but the pet doesn't act like the original did. So tracking spells apparently have nothing to do with a person's DNA, other factors must be at work. Also since she is possessed is Justine the same woman she was before so was the attempt to track her doomed from the start?