The American writer, best known for her series of books about fictional medical examiner Dr. Kay Scarpetta, is suing over allegations her multi-million dollar fortune has vanished.
She claims to be missing up to $40 million (£25 million) and has accused executives at New York-based company Anchin, Block & Anchin of mishandling her finances, making bad investment decisions and over-billing her.
The case has gone to court in Boston, Massachusetts and Cornwell was in attendance this week (beg14Jan13) when lawyers for the defence began detailing her spending habits in their opening arguments.
James Campbell, an attorney representing Anchin, Block & Anchin, claimed Cornwell spent the missing money herself and alleged the author and her partner, Dr. Staci Gruber, frittered away the fortune by lavishing $5 million (£3.1 million) on a private jet service and $40,000 (£25,000) a month on renting a luxury apartment in New York City.
He told the court, "Where did the money go? Ms Cornwell and Dr Gruber spent the money. You have to consider the large lifestyles involved, the spending habits, impulsive buying."
In the lawsuit, Cornwell acknowledges her struggle with bipolar disorder, and claims bosses at the firm were aware of her illness and abused her trust.
Cornwell's lawyer, Joan Lukey, argued, "This case is, at its core, about trust. There is no amount of money that is enough to properly compensate her for what Anchin, Block and Anchin did."
Angelina Jolie is said to be starring in a big screen adaptation of Cornwell's book series, playing the author's most famous character.