The family spokesman, David Marriott, said Knox did not agree to attend and there is no requirement she be there.
Italy could request her extradition from the United States, CNN said, but it is not clear whether the United States would extradite Knox.
Knox spent several years in prison in Italy, after she was convicted of killing 21-year-old Meredith Kercher, an exchange student.
Kercher was found stabbed to death in November 2007 in the villa she rented with Knox.
The convictions of Knox and her ex-boyfriend, Raffaele Sollecito, were overturned in 2011 due to lack of evidence.
Knox then returned to her hometown of Seattle.
But last year, Italy's Supreme Court decided to retry the case, and that evidence could support the argument that Kercher was killed in a twisted sex game.
Knox denies those allegations.
Knox and Sollecito's retrial is expected to start this fall.