I Am a Young Widow Forum & Chat Board | Need Advice on how to handle son's grief

My wife died a year and a half ago on Christmas Day. We have a 6 year old son. His grandmother (wife's mother) continues to make every event, holiday, birthday all about her daughter not being there with my son. For his birthday she gave him huge picture albums of my wife, for Christmas it was ornaments with her pictures, books about the loss of his mother etc. I understand that she is still grieving the loss of her daughter but I do not want my son to be reminded for every celebration that his mother is not here with him. I don't want him to associate Christmas with the loss of his mother. I want him to be giddy with excitement for every Christmas and Birthday. My son and I talk freely and openly about his mom so I don't feel like I need to push talking about her on certain occasions. How do I approach this matter with my mother in law?