Sister vs predicative case

Sister

noun
  • Title of respect for an adult female member of a fraternal/sororal organization, or comrade in a movement, or even a stranger using fictive kin. 

  • A title used to personify or respectfully refer to concepts or animals. 

  • Title of respect for an adult female member of a religious order. 

predicative case

noun
  • A term that may sometimes be used to describe the case marking a predicative nominative (a noun that renames the subject often following a linking verb), or for the adjective that agrees with it (predicative adjective). 

How often have the words Sister and predicative case occurred in a corpus of books? (source: Google Ngram Viewer )