I haven't seen she kill anybody but walkers. Ron have not kill zombie and anybody. He planning to kill carl cuz his jealousy and lost his father. In comic ron and carl wasn't teenager. Enid not existed in comic. Ron upset carl was unsympathetic about Ron's telling him Rick killed his father.
Perhaps the writers introduced the character of Enid to finish off Ron. She survived for a time after her parents' death and she would likely be more willing to kill anyone for survival, including Ron. She knows how the world is and what's necessary to survive.