To Clarify... (spoilers)
This is what I got from the movie in a nut shell:
The dad was sexually molesting his daughter; the mother finds out and is understandably upset, but doesn't contact the police. The mother loses her mind and eventually ends up "wrapping her car around a tree". The daughter is upset about her mom dying, blames the father for causing her death and is upset about what he did to her.
Mom's vengeful spirit haunts the dad to keep him away from the daughter. Near the end of the movie the spirit hears the dad's lies while the doctor is interviewing him and goes berserk.
The scratches on the daughter's legs could be attributed to the dad molesting her even after the mom's death.
Notice how most of the paranormal activity is directed towards the dad: thrown through the glass door and thrown up against the wall etc etc.
What you guys think?