She looks amazing at 81. But she went to prison for dumping stocks based on insider information she got from her stock broker. You are not supposed to do that, although I'm sure it's done all the time on a much larger scale by Wall Street insiders, who are not inclined to blab about it to someone else. She was the really small fish in a pond full of much bigger fish, but an easy catch that didn't harm the bigger fish.
When she went to jail, stock prices in her own corporation went down because of a potential management vacuum I guess. My brother-in-law bought a bunch of stock in Martha Stewart Inc., and then he sold it at a nifty profit when she was released.