I am totally enjoying this season. I like the character development and how episodes are centered around just a few characters. They will all (or most) meet up again either at Terminus or somewhere.
Lizzie didn't go bonkers from the apocalypse, she was already there prior to that. She was a sociopath, couldn't tell good from bad, right from wrong. She was hard-wired "off kilter" from the get go. The apocalypse pushed it to the forefront sooner but she was gone prior to it.
She wasn't sorry she killed her sister she was sorry that she pointed a gun at Carol and she was sorry only because she thought Carol was mad at her.. She had NO CLUE that the walkers were dangerous she just thought they were different ... kind of like how she is different. No remorse or sense that killing her sister was wrong or that killing Judith would be wrong. When Lizzie said "I know what I have to do" I thought she was either going to try and kill Carol and/or Tyrese but mostly I thought she was going to kill herself to show everyone how the walkers were fine, just different.
TOTALLY didn't see Lizzie killing her sister scene at all but did see that Carol needed to tell Tyrese that she killed Karen. She had to tell him. Wasn't that scene great? Carol did what needed to be done but she was sorry she had to do it and T saw that, which is why he forgave her. He's not going to seek revenge or anything like that. It is was it is and he knows it. I literally mouthed "I forgive you" right before he said it.
Carol, the meek, weak, and abused person we met in season one has turned into one of the strongest, gutsy-ist, self-assured characters. So glad she is back.