gentlewoman vs queen mother

gentlewoman

noun
  • A woman of the nobility. 

  • A female member of a legislature, especially a female member of a House of Representatives. 

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 gentlewoman and queen mother occurred in a corpus of books? (source: Google Ngram Viewer )