The TV series was never going to be like the comic and that was said from the get-go. It started pretty similar, but Kirkman has said dozens of times that he is writing two different things. If you keep comparing the show to the novels you are always going to be disappointed IMO so you should stop doing that.
The problem is, I shouldn't be disappointed when I compare the show to the comic I've been a fan of since day one. The show should measure up. They were obviously never going to follow the comic word for word, but the quality should still be there. Don't get me wrong, I liked the better part of the first 2 seasons, but season 3, and so far, season 4, have been lackluster.
There's also no excuse for making unnecessary changes to main characters the way that they have, even killing some that are crucial to the story. They killed Dale without even doing the cannibal story-line, which explored the lengths some people are willing to go in this new world, and the toll is has on the psyche. They skipped over the winter, which presented some interesting obstacles to the survivors and walkers alike. They killed Lori and Andrea before their time, both of whom are important to Rick's character progression.. I could go on, but I'm not trying to bash the show. It's just hard for me not to draw comparisons, when they keep throwing in these nonsensical changes that detract from the quality of the show.
Andrea is by far one of the most important characters in the book next to Carl and Michonne. At least up to the Alexandria Safe-Zone thats as far as I know right now lol.
Honestly the only good addition to the show is Daryl but he has taken the role of Andrea i guess.