[j7ake]

That won’t stop her from being a billionaire. She could have ownership of a company that would make her net worth orders of magnitude higher than any earnings cap.

You cannot put a cap on a company’s worth, because it’s a guess.

They can decide to nationalise those companies as well, but then she could take her skills to another country. Then that country loses all of her earnings for sure.

The other way to stop her from being filthy rich would be to make people stop liking her books. Which at this point one should ask how much damage one is willing to do to stop a person from being rich.