Writers usually have to hit milestones to collect all of the money.
Publishers just dont dole out $12 million dollars up front, its a marketing ploy.
Which each milestone more of the money is released. So they can say $12 million but if the book sells 50,000 copies - the writer isnt getting all $12 million. It depends on how the book sells.
So $12 million means they publisher thinks they can sell 12 million copies. If it only sells 1 million copies, the author only gets a small percentage of that $12 million. Otherwise book publishers would go out of business rather quickly.
The money isnt in books, its in the rights to the story that could later be resold for a movie or television show. And she probably wont get to keep those rights.
Even if she gets $2 million, she will have pay your taxes on it, and pay her agent and lawyer... that $2 million dollars advance ends up being about $800,000 - if - she gets all of it. Again not exactly retire now money.
Lewinsky had to go back to school to get a degree in economics and also had to set up her own brand of high end hand bags.
Here's what Monica Lewinsky is up to 20 years after the Bill Clinton affair - Business Insider