Crone vs queen mother

Crone

noun
  • One of the triune goddesses of the Lady in Wicca alongside the Mother and Maiden, representing an old woman. 

queen mother

noun
  • A widowed queen consort (a queen dowager) whose son or daughter from that marriage is the reigning monarch. 

How often have the words Crone and queen mother occurred in a corpus of books? (source: Google Ngram Viewer )