Please put comic spoilers in spoiler tags. Thanks!
That's not a comic spoiler, it was on the show. Or are you thinking of what's to come? (I have no idea, though it's not too hard to put two and two together at this point.)
Not only that, but someone should have yelled at Andrea for the noise that a gun shot makes.
If they're concerned about that, why is she on lookout with a gun in the first place? She waited to shoot until the guys inexplicably stopped in front of the zombie and didn't attack him. At that point, she might have wondered if they were in trouble - maybe they saw a wave of zombies in the woods behind the first and were in shock?
This may have to do with my opinion that it's insane
to get close enough to a zombie to fight it hand-to-hand, especially if you are close to an area where other zombies might be hidden by trees etc.