Not everyone reanimates quickly. It took Amy all night long and into the morning before she came back as a walker. The guys in the bar may well stagger back to life.
Actually, Lori plotting against Shane is the first thing she's done that makes sense. It may be sneaky and underhanded, but she isn't that far out in left field to be worried about Shane's possessiveness. And he did leave Otis behind to die a horrible death. Shane's a ticking time bomb. Still, they needed a different actress for Lori. Another actress would have elicited more sympathy. I like the actresses for Andrea, Maggie and Carol. I didn't feel the Carol/Daryl scenes were "meh." She gets him. After all the abuse she took from Ed, Daryl lashing out for more understandable reasons is a piece of cake for Carol with the shitty life she's had. I like Daryl, even though he was being a mouthy mofo.
Also, appropos of nothing, with the whole group of them there in the house and concerned about whatshername who's sick....it's not entirely unrealistic that they wouldn't have noticed one of the cars was gone.