I believe Lizzy is infected. Here's why: when Saul and burt entered the furniture store Saul remarked how bad it smelled. Now it being a furniture store there shouldn't be anything in there to rot. Also none of the mallers said anything about it smelling bad. So what changed lizzy threw up all over the place. Normal puke isn't going to stink up the whole store. But if her insides were slowly rotting? We all know the zombies have a horrible smell. Just throwing it out there