mother-in-law vs stepmomma

mother-in-law

noun

  • The mother of one's spouse. 

  • A mother-in-law sandwich. 

  • A mother-in-law apartment. 

stepmomma

noun

  • stepmother 

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