articles - "She's the author of" or "She's author of"? - which one is correct?

What's the difference in the usage of the article "the" with the word "author"? Why is the article "the" left in the second sentence?

She's the author of "The Power of Glamour," "The Future and Its Enemies" and "The Substance of Style."

She's author of the new book, “The Intimidation Game: How the Left is Silencing Free Speech.”