Sweetpea by C.J. Skuse
The lead character works a tedious journalism job by day. She survived a horrendous crime in her youth and had some training for survival by her father. She makes a regular "hit list" of people that have wronged her or others in various ways (from pedophiles to people taking too long in the checkout line.) She becomes the casual serial killer. Easly in the book she castrates a drunk that was coming onto her and pushes him to the river, only to return back as if nothing happens. She gets involved in other crimes. She later frames someone else for the crimes. The book has light, vulgar tone with plenty of dark humor.
