Miracloman wrote:My only possible justification for her reaction would be she was shocked to hear him pretty much say that "I killed him and I am glad I did it".For all of her messed up personality(I am trying to be gentlemanly here) she knows that Rick is a decent person and his career as a cop aside,he is not one to kill in cold blood.And although he (imo) did not perpetrated cold blood murder,to her may have been shocking and perhaps horrifying to know how far he could go.But even so such justification can just go so far as to excuse her attitude.
But before Rick said that he was "glad it was over," he explained that Shane took him out into the woods with the intent to kill him. He explained that he kept giving Shane the opportunity to turn around and head back but Shane kept taking him further and further away. Like he said, there came a point where he knew that only one of them was making it back to the farm that night. This isn't even taking into account the 2 other times that Shane tried to kill Rick that Lori also knew about. This isn't like Rick suddenly decided that Shane was too dangerous and took him out back to put a bullet in his brain and then rejoiced because it was over. Rick was exhausted both physically and mentally because Shane left him no other choice.
On the Talking Dead, both Robert Kirkman and Glen Mazzara admitted that Lori wasn't even mad at Rick, she was mad at herself because she knew that it was her fault.