So this morning I was figuring out Catherine's story and how she died. So Ill explain it after i put a pic of the two up.

So Sadie is Catherine's fiancé, well was. The two were looking at houses to buy and one happened to be haunted. They didn't know. Some backstory with Sadie, she has always been a little jealous of Catherine's looks and that brings her downfall. A ghost happened to get into Sadie's head and manipulate her, causing her to kill Catherine. Catherine became a vengeful ghost, who can only rest if she kills her murderer. Two problems with that.
1. She can never bring herself to fully kill Sadie
2. Sadie knew about the poccession and killed herself shortly after, passing on instead of staying.
That means Catherine is forever stuck in our mortal plane. Her spirit thrives on grief and anger.

Yeah, its bad but hey, it sounded better in my head.