Little is actually known about Delia before her first appearance in Blue Eyes (featured in the Sin City Yarn "Lost, Lonely, & Lethal) other than she was one time the girlfriend of a man named Jim whom she picks up and Kadie's and kills him by breaking his neck after having sex with him.
The only other bit of information about her past is that some time after her and Jim split up she marred a man who beat her and she finally killed him up on which she discovered that she actually liked killing people and set out to be an assassin for the Wallenquist Organization. Killing Jim, the only man that shes ever truly loved was her final test which she passed.
She is told that she will need a Code Name and she picks Blue Eyes a nick name given to her by Jim.
She later appears in another starring role in "Wrong Turn" where she kills a man by mistake thinking that he is her Target, again after taking him to The Pits and having sex with him.
"Wrong Track" Takes place after "Wrong Turn" where Delia tries to catch up to and kill her actual target. She manages to catch him on a train and after having sex with him kills him.
This leads the Colonel to ask her "Delia...do you intent to have sex with all of them?" to which she replys "Only the ones I like."
Delia is finally killed by Wallace in "Hell and Back"