This was another personal barrier that came down for Kate. I wouldn't be too hard on her for making the decision go to Rick's house. Also if we look at it another way, for the first time in a long time, she has something and someone to be with and spend time with at Christmas time now. In a way she has a new family, something that is somewhat new to her and that she's still getting used to. Also Alexis and Martha also cancelled their Christmas eve plans to be with Rick.
The last shot of them framed in front of the Christmas tree was simply awesome. Now I can spend the hiatus and catch up on what I missed