JK Rowling is +$1 billion for the books and royalties on the whole "Harry Potter" thing. But that is clearly an outlier. My sister has a published book and she hasn't made shit.
Has you sister made a living off of being an author, or does she do it on the side?
Tom Clancy is another dude who probably made a killing
Who wrote the Bourne books?
Author who created lord of the rings.