Sady Doyle tries to answer that question with this article titled "The Violently Killed Femmes".
It comes down to the vulnerability that we perceive in a young (almost always white) woman with an air or innocence and virginity. In many shows it transpires that this may not be the whole truth. Twin Peaks' Laura Palmer is a typical example of this, the prom queen who snorts coke and hangs out with demons. Nonetheless she is a complex and ultimately sympathetic character, especially compared to other examples where the dead body is there to be both mourned and fetishised in equal measure.
