Date: Probably 2000+
Genre: Horror, thriller.
Country of origin: Probably the U.S., mostly caucasian actors.
It begins with a small girl, who's parents were murdered by a serial killer.
The story jumps ahead to show her as a young adult, working as some sort of private teacher/nanny for a family of five (parents + 2 girls, 1 boy).
Mysterious killings begin to happen in the area (maybe with a hook as the murder weapon) and she becomes very scared.
In the end it's revealed that she was the murderer, she was somehow traumatized into doing it by her childhood tragedy.