They had to end it that way. As bad as it was they still need a "cliffhanger" and it's what will happen with the Governor situation. They had no build up for anything else to make a last ditch effort. Andrea is annoying but she was a very important character in the sense that some people who don't know how to lead think they do. She was there to keep people trying to figure out direction. I mean let's face it other then Daryl and Glen, Andrea is one of the few long term actors who had any legitimate character development.