Amanda Knox wept on television as she vowed to fight her latest conviction for the murder of Meredith Kercher "to the very end".
Knox broke down several times in the TV interview and said: "This really has hit me like a train."
She made it clear she would never voluntarily return to Italy to serve the 28-and-a-half year sentence handed down by a court in Florence.
Knox was in her hometown of Seattle when she learned her conviction for killing the 21-year-old British student had been reinstated by judges.
Amande Knox broke down as she was interviewed on abc's Good Morning America
She spoke to ABC's Good Morning America after Miss Kercher's brother said Knox should be extradited to Italy by the US.
Legal experts say there is no reason why the US should refuse Italy's request - meaning Knox could be jailed in Italy.
Knox's ex-boyfriend Raffaele Sollecito was also found guilty after judges ruled the pair should not have been cleared on appeal in 2011.
Knox is consoled by interviewer Robin Roberts
She sobbed as she described hearing the news live via an internet link to an Italian TV network.
"My first reaction was 'no' - this is wrong and I'm going to do everything I can to prove that it is.
"But it was only on my way here that I got my first cry."
Exchange student Miss Kercher lived with Knox
Knox, 26, said she had contacted the chaplain at her former jail and he had reminded her that "people still believe in me".
Asked if she was prepared for any extradition she replied: "I'm not."
She added: "I will never go willingly back to the place. I'm going to fight this until the very end. It's not right, and it's not fair.
"This really has hit me like a train, I did not expect this to happen. I really expected so much better from the Italian justice system. They found me innocent before - how can they say this is guilt beyond reasonable doubt?"
Asked what she would say to the Kercher family she said: "I have sent them a letter - it's in the mail.
"I just want them to know I really understand that this has been incredibly difficult - that they too have been on this never-ending thing and when the case has been messed up this much then a verdict is no consolation."
Members of Ms Kercher's family were in court
Lyle Kercher, Meredith's brother, said: "If somebody's found guilty and convicted of a murder - if an extradition law exists between those two countries - I don't see why they (the US) wouldn't.
"It would set a difficult precedent if a country such as the US didn't choose to go along with laws they themselves uphold when extraditing convicted criminals from other countries."
Sollecito, who was not in court for the verdict but had attended lengthy hearings earlier in the day, was sentenced to 25 years.
Sollecito is in Italy but was not in court for the verdict
The 29-year-old has been held by Italian police after being stopped near the country's border with Austria on Friday morning.
Lawyers for Knox and Sollecito have said they intend to appeal to Italy's highest court and a long legal battle for Knox's extradition is expected.
Miss Kercher's sister Stephanie told reporters she would not read a letter Knox wrote to her until the appeals process is exhausted.
"I am told there was a letter - I have not physically seen it ... I don't have a need to read it at the moment."
She also said she did not want to meet Knox, who reportedly has tried to make contact with the Kercher family.
"It's not something we would want to do at the moment - and I can't say we ever will. Regardless of a guilty or not guilty verdict, a lot has happened over this amount of time."
Lyle Kercher told Sky News he could never forgive those responsible for his sister's death.
"I think you'd have to be a very strong-willed - arguably religious - person to find that forgiveness," he said. "I think it is so easily forgotten what happened to Meredith.
Amanda Knox leaves her Seattle home after the verdict was announced
"When I read reports even now, I find myself skimming past the paragraphs that refer to what actually happened to her because it is so horrific."
Knox and Sollecito were charged in 2007 after Miss Kercher's semi-naked body was found with her throat cut in the bedroom of the house she shared with Knox in the central Italian city of Perugia.
The Leeds University student from Coulsdon, Surrey, had been sexually assaulted.
Two years after the pair were found guilty at their original trial in 2009 - and handed jail terms totalling more than 50 years - the verdicts were overturned and both walked free from court, with Knox returning to the US and going on to sign a book deal.
The verdicts being delivered in Florence
Their acquittals in 2011 came after a damning 100-page report outlined a catalogue of errors and breaches of procedure that had been made in collecting evidence.
The third trial began last September in Florence.
After nearly 12 hours of deliberations on Thursday, the court upheld the 2009 convictions.
In an interview recorded before the latest verdict, Knox said the court's decision meant she was now technically a fugitive.
"I'm definitely not going back (to Italy) willingly," she said. "They'll have to catch me and pull me back kicking and screaming."
Speaking to The Guardian, Ms Knox said her memory of what happened on the night the murder was clear.
Amanda Knox prepares for the interview
"I knew what I did that night," she said. "I very clearly remembered what I did that night. That I was with Rafael, we had dinner, we did what we always normally do when we're all the things we do when we're together.
"But they started questioning me about that, making me doubt what I was telling them. I kept telling them, 'look, I don't know what time I was doing things.
"All I can tell you is I left my house, me and Rafael went to his house, we were hanging out, listening to music, I read some Harry Potter ... I remember reading emails, we talked, we had dinner; that's what we did."
Though Knox has remained in the US, she emailed the court to protest her innocence in a statement read out by her lawyer in which she insisted she ''was not a monster".
Drug dealer Rudy Guede was sentenced to 16 years over Miss Kercher's murder. Investigators said he did not act alone.
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