daughter dies or goes missing on a camping trip and the son fakes a ghost for the mom.  During the investigation they find out that the couple she baby-sat for had some sort weird sex thing with her.  in the end they figure out the son has faked a ghost to help his mother who is distraught about the daughter.   As they are moving and finally leave the house it’s revealed that there was really the ghost of the daughter lingering.

This is at least 5 years old i believe.