aunt-in-law vs niece

aunt-in-law

noun
  • The wife of one's uncle or aunt (parent's sibling). 

  • The aunt of one's husband. 

  • The aunt of one's wife. 

niece

noun
  • A daughter of one’s cousin or cousin-in-law 

  • A daughter of one’s sibling, brother-in-law, or sister-in-law; either the daughter of one's brother ("fraternal niece"), or of one's sister ("sororal niece"). 

How often have the words aunt-in-law and niece occurred in a corpus of books? (source: Google Ngram Viewer )