Now I prefer to believe the latter. Better to portray Shurpanakha as a complex character (After all, she is the granddaughter of a Saptarishi). She shouldn't just live for lust!! Even Kaikasi had her own intentions for marrying Vishrawas.
Originally posted by: Vibhishna
From what I know, Shurpanakha's husband was killed by Ravana after the latter discovered his schemes for obtaining power and declaring war against Ravana himself. In a moment of rage, Ravana killed his brother-in-law. When Shurpanakha came crying to him, he regretted his actions but consoled his sister saying he had to do it.
He sent Shurpanakha to Dandakaranya where their cousins Khara and Dusha reigned to help her get over her misery.
Shurpanakha's son was residing in the Dandaka Forests doing severe penances to please Indra or Lord Brahma - don't remember which. A divine being (Yaksha or Deva - not sure again) gave Lakshman a new weapon saying it held immense power. Lakshman decided to try it out on a dilapidated hut and was aghast to find blood gush out after a few seconds. It was the same hut where Shurpanakha's son was dong penance.
Shurpanakha bent on revenge went forth to where Ram, Lakshman and Sita were residing but fell for the handsome princes.
There are some versions which claim that Shurpanakha instigated Ravan against Ram to bring about his end as revenge for killing her husband. I don't know which version they are.