leading lady vs principal character

leading lady

noun
  • A woman who does or can play the lead role in a movie, play or other production; a woman who frequently plays such roles. 

  • The type of conventionally beautiful and approachable woman who is perceived as being capable of playing female lead roles in movies or other productions. 

principal character

How often have the words leading lady and principal character occurred in a corpus of books? (source: Google Ngram Viewer )