This movie has a woman who gets raped and killed then comes back as a angel. She then helps her sister because she knows she will soon be raped as well. The Ghost falls in love with a man from town but at the end she killed the rapist

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I Know Who Killed Me (2007)

I Know Who Killed Me (2007) - Plot summary (http://www.imdb.com/title/tt0897361/plotsummary)