Who is Nana from Florida from Mick Harte Was Here and what is their importance?

Nana from Florida is Phoebe's grandmother. She comes and stays with Phoebe and her family after Mick's death. Nana cooks spaghetti one night and insists that the family eat at the table together. When she sets the table, however, Nana mixes up the spots where family members generally sat. Because they are no longer concentrating on Mick's empty chair, Phoebe and her family begin to eat together at the table again.