Have you noticed that Christmastime through early January seems to produce a higher frequency of death and loss than at other times of the year? This phenomenon adds more emotion to a season already loaded with it.
The biggest thing I've noticed coaching people who have suffered a loss is that they underestimate its effect as well as the time required for life to return to normal, albeit a new normal. Grief challenges one's emotional equilibrium. It can commandeer thinking and impede daily functioning.
A character in my novel would've found this website helpful. It includes a brief summary of the five stages of grief - denial, anger, bargaining, depression, and acceptance. The video at the top of the page is excellent.