Lizzie will become the comic version of the boy who killed the cats then killed the other boy (think it was actually his brother). He was later shot and killed by Carl. I'm thinking that Lizzie will either kill Judith (too obvious after last nights episode) or more than likely the other little girl, Mika her sister. Then at end of the season Carl will shoot at Lizzie, but Rick steps in the way to stop him and gets shot and killed instead. I know we were already promised "something big" to happen this season and that's my thinking...
All the clues and build up (so far) are there. (Killing of animals, hand over Judiths mouth, being willing and able to kill)