Wrong assumption
Wa-- okay, time to get to the bottom of this.
Did the family directly eat the ashes, thinking they were something else? Did they eat the ashes at all? Is anything else they ate relevant?
Is the use of 'spoonful' significant? Does it mean actually using spoons? If so, is the use of spoons significant?
Is there one other relevant person, or multiple? Does it matter?
Is/are the other relevant person(s) biologically related to the grandmother? The family? By marriage, to grandmother? To the family?
Is/are the other relevant person significantly involved in how grandmother's eatenity came about? Did they intend for it?