The title for this comes from some offhand remark of our heroine's grandmother back in the 1950s. So it really doesn't have much to do with anything except to give us some sense that it happens in the south among gracious or would-be gracious people.
The book goes backward and forwards between the 1950s / early 1960s memories of the heroine and the "today" of 1972-1974 when she's kind of picking up the pieces of her and her siblings' lives.
I didn't really care about the 1950s or the bad early family history, because I was impatient to find out about what happens in the here-and-now.
What happens in the final chapters of the book is probably bittersweet, so I guess the title speaks to that.