maternal cousin vs stepsister

maternal cousin

noun
  • A child of one's mother's sibling 

  • A more distant relative of one's mother who is not a direct ancestor 

stepsister

noun
  • The stepdaughter of one's parent which is not one's half-sister. 

  • The daughter of one's stepparent who is not the daughter of either of one's parents. 

How often have the words maternal cousin and stepsister occurred in a corpus of books? (source: Google Ngram Viewer )