Dead Write (2007)

After driving husband Martin to infidelity and catching him at it, mentally-unstable author Jade returns to her New Zealand home to write a book based on the town's history, helped by the local schoolteacher and her college thesis protégée, and also visit her father Christopher. As her editor later explains, her suspicions concerning ever more locals stem from a pathological mental condition. However, more then just paranoia comes with the horse-riding incident that killed her ma, that causes obsessive guilt for her and her father.