It was granny who told it to Mary straight, after Matthew died in a car accident: Either you choose to live or you choose to die. Obviously Mary chose to live and she will be back for the fifth season. The plot line will probably chronicle what her suitors are up to.
In addition, it was granny who saved the Earl's marriage when Cora blamed him for their daughter's death in childbirth.
Well, Smith is 80 years old. She is a role model for all of us who are determined to keep working.