Lawyers for Amanda Knox described her as "very worried", as Italy's top court is due to issue what could be the final verdict on the 2007 murder of British student Meredith Kercher.
Knox, who was sentenced to 28.5 years in jail by the Florence appeals court for the killing of her former roommate last year, was awaiting the ruling in her hometown of Seattle, US.
She is "worried, very worried," said her attorney, Carlo Dalla Vedova. "I don't think she's sleeping much."
The Court of Cassation in Rome is to decide whether to uphold her conviction or throw it out ordering a new appeal trial.
Judges could also partially quash the appeals verdict, amending it without ordering a retrial.
Knox's ex-boyfriend and co-defendant Raffaele Sollecito was in court as the final hearing got underway. "I'm here all day, also tonight," he said, as a verdict is expected late this evening.
The Italian is also facing the prospect of a lengthy prison sentence, as judges are similarly deciding whether to confirm his 25-year sentence over the murder.
Kercher, from Croydon, south London, was found with her throat slashed inside the apartment she shared with Knox in the university town of Perugia, central Italy, on 1 November 2007.
Prosecutors say she was killed by Knox, Sollecito and Rudy Guede, a drifter from the Ivory Coast, after an argument.
Guede was sentenced to 16 years at the end of a separate trial and is serving his sentence in Viterbo jail, near Rome.
Knox and Sollecito have always maintained their innocence. After a series of appeals and opposite rulings that polarised public opinion, they were found guilty of murder in January 2014.
Last summer the lodged an appeal with the Court of Cassation, the last available in Italy's criminal justice system.
If the Court of Cassation were to uphold Knox's conviction, Italian authorities are expected to initiate legal proceedings to extradite her from the US.
Update - 14.40 GMT Wednesday 25 March
The court has decided to postpone part of the final arguments and the verdict to Friday 27 March.