she's dead because she was dared to spend the night in a graveyard, at the site of one of the most common ghost sitings. she didn't believe the stories. she thought they were foolish. she was required to take a knife and plunge it into the grave to prove she had been there. poor girl didn't realize she had plunged the knife right into her dress. sadly when she started hearing voices, she got scared and tried to run. but the knife prevented her from going anywhere. her fear and paranoia eventually became to much and she succumbed into eternal darkness.
This reminds me of an old episode of the twilight zone. A man was supposed to go to his arch-rival's grave, who had pledged to grab him from underground. So he goes, and his friends tell him to plant his knife in the soil as proof he was there. So he bends over, plants the knife, but when he gets up to leave, he falls over. His friends find him dead of a heart attack. At first they figured that he stuck he knife through his coat, and when he got up, it tugged and scared him so badly his heart gave out. But, then one pointed out that the way the wind was blowing, his coat would have been blowing away from the grave, with no way he could have put his knife through it.