I thought it was pretty obvious that all signs point to Lizzie as being the one to kill Tyrese's girl and the other dude, not Carol and her being the one feeding the rats and doing any dissecting. The naming of the zombies, the playing in the pool of blood with her foot after someone died from the virus a few episodes back, her leading the infected zombie away almost like a dog (here boy, come here boy), the small handprint Rick found and as seen last episode, she's one hell of a ******* shot.
That girl has future serial killer written all over her. She'd be perfect for Carl.