Saw this on cable a long time ago, details are fuzzy. Some things I remember:
Like the title says a teenage girl starts suspecting something is not right with her father’s “girlfriend”.
She sees the girlfriend having sex with someone else (I think it was the girlfriend’s “brother”, but it’s not really her brother we find out later, when the scam is revealed)
The teenager had a friend helping investigate and the friend is run down and killed by a car.
Towards the end of the movie the evil girlfriend is killed by electrocution (improvised trap involving the electrical panel and water).
Anyone know what this movie is? Or did I dream it. lol