I agree that the Italian courts apparently have a tendency to arbitrarily violate their own laws and constitution, and of course ECHR case-law, based on what we have seen in the Knox - Sollecito case.
Suppose that, contrary to Italian law, a civil suit against Amanda or Raffaele for the murder of Meredith succeeded in finding one or both liable. They could appeal that verdict. A civil verdict in Italy may be appealed to a second-instance court, and eventually to the CSC (civil division). In the case of appeals, only the final verdict of the CSC is definitive.
Would a US court make a foreign civil judgment enforceable against someone resident in the US? That all depends. Here is some information:
https://www.law.cornell.edu/wex/comity_of_nations
Again, a US court would review the laws of Italy and find that the civil trial had violated Italian law, as previously discussed. The acquittal ended any legal civil case against Amanda Knox in Italy and this would mean the US court would not accept the illegal Italian civil judgment. The lack of fairness and the clear presence of fraud in the police procedures and Massei and Nencini trials, as partly acknowledged by the Marasca CSC panel motivation report, would also argue against the US court accepting the illegal Italian civil judgment.
Note that if the US court looks for fraud in the case, it would be examining the details of how the trial was conducted and the reliability and meaning or interpretation of the evidence.
So I continue to believe that any civil action in Italy, or its acceptance by a US court, is simply not going to happen. The case is over, with the exception of some issues such as the ECHR considering the application Amanda has lodged against Italy and a potential revision trial. There is also the matter of compensation for miscarriage of justice. There could be grounds for other ECHR applications by Raffaele or Amanda.
I suspect Italy will let the calunnia against the police charge expire due to statute of limitations, but we shall see.