Above a certain level I could certainly get behind saying no she's not entitled to it. 100% marginal tax rates above $10 million in annual earnings seem perfectly reasonable to me.
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.