Was it "To Die For," starring Nicole Kidman? This is the one she did a few years ago, loosely based on the Pamela Smart murder trial in New Hampshire (schoolteacher befriends outcast high-school kids, has an affair with one of them, convinces him to kill her husband; pretty sordid little black comedy, but a good one). I'm not sure this is the movie it's from, but it rings a bell.