In the story, Granny said, "What was it? Something not given back...." What wasn't given back?
When Granny was dying "she had changed her mind after sixty years and she would like to see George." She wants her daughter to find him and tell him that she "forgot him," that she had a husband and had "fine children out of him. Better than I hoped for even." She wants him to know that she "was given back everything he took away and more." The something that was not given back was her chastity, which George took from her. What he gave her instead was a feeling of guilt; this guilt stayed with her for her entire life. No matter how "clean and folded away" her linens, brushes, and bottles were, the dust of her guilt would always fall around her.
As Granny is dying, she remembers the time she was jilted by the man she loved, George. He left her standing at the alter fruitlessly waiting for him to show up. She was extremely humiliated and hurt. What George took from her was her pride, her self-esteem, and her ability to enjoy a completely happy life free from bitterness. Even though she married another man and had children and had a good, long life, she never got over George's jilting of her and she never was able to forgive him. Thus, she is left bearing this anger and humiliation as she is dying and therefore cannot die in peace.