Frustrated that Carrie has insisted on tagging along for a school assignment, Mary and Laura fail to keep a close eye on her. They live to regret this when the little girl wanders off and falls into an underground mine shaft.
Emotionally distraught after her little girl has fallen down a mine shaft, Caroline Ingalls instinctively blames someone else (in this case, Miss Beadle). Even considering the magnitude of the situation, this is incredibly out of character for Caroline, and you never see her do such a thing again.