Now I understand........

While I was in SD I read HALF BROKE HORSES by Jeannette Walls, the author of THE GLASS CASTLE. It is a good read and helps make some sense of the mother in GLASS CASTLE. HALF BROKE HORSES is the story of the grandmother, i.e., the mother of the mother, in THE GLASS CASTLE. If you've read CASTLE then I think you will particularly enjoy HALF BROKE, though it would be good on its own.
So many good books, so little time.