mammy vs old woman

mammy

noun
  • mamma; mother 

  • In the southern United States, a black nanny employed to look after white children; or in the antebellum South, a female slave who was close to the household and looked after the children. 

old woman

noun
  • One's mother. 

  • One's wife. 

  • An elderly woman. 

  • A person (irrespective of age or sex) who is always complaining about his or her situation. 

  • The plant sea wormwood. 

How often have the words mammy and old woman occurred in a corpus of books? (source: Google Ngram Viewer )