I will assume you say that because you do not believe the Spirits of the Dead can speak back to us here on earth.
They can not only speak to us from beyond the veil of death, they can appear to us anytime they want to in our homes or anywhere they choose and come into our dreams and give us pleasant dreams and or nightmares.
When the person dies, their spirit leaves their body and takes with it all its intelligence and memories both good and bad and if they choose to come back and seek vengance there are many ways they can do that including getting into the thoughts and having the human do many things both good and bad and if they wish to go further they can climb into the body and become possessing spirits seeking vengance and if that happens then a Priest is called into to try to reason with the spirit and remove it.
Having said that I don't think Stacy is the kind of person who would choose to sit in the smelly body of Drew among the entrals and other unpleasantries but there are some spirits of the dead who are not as fastidious and when that happens the Human they choose to haunt and or poss can have quite a time trying to find a solution.
