Again, she doesn't need to be "kept in line." She chose to kill by herself. She killed by herself despite the Batclan or Vic's best efforts to stop her. She chose to stop killing by herself, in isolation from any member of the Batclan at a time when she hated all of them. Their presence, absence, or input makes no difference whatsoever to her decision to kill or not to kill, which is entirely her own, completely unaffected by anything that has changed in the DCU between the end of Birds and now, and has long since born no resemblance whatsoever to what we see here.