system
Given the following post, respond as if you're commenting on Reddit:
human
[Injustice: Gods Among Us] Why didn't Superman kill Harley Quinn?

When Superman went to rescue Lois, he found both Harley and the Joker performing the surgery that would implant the bomb in Lois' body. They were both directly responsible for the death of Superman's family and Metropolis, so why does she get a pass?
gpt
Well, a small part is that when she's not under the Joker's influence, Harley isn't really all that bad (as indeed the next few years show). Everyone knows that Joker is the leader there and she was going along with him.

Mostly though he just didn't know here she was. Batman had Joker in interrogation - Supes flew there and killed Joker right away. Harley was being driven away by cops. As soon as she heard Joker was dead she killed the cops, stole the car and went into hiding. The police radio indicated that Superman was indeed looking for her to kill her. 

Then Arrow found her and hid her. By the time Supes saw her again a good amount of time had passed and in most of their meetings she had taken a green pill and so was hard to kill.