Amanda Knox has successfully appealed her conviction of murder in Italy. She is now on US soil and therefore under the protection of US laws.
The Fifth Amendment of the Constitution states that; "Nor shall any person be subject for the same offense or to be twice put in jeopardy of life or limb". To extradite Ms. Knox to Italy would violate her Fifth Amendment right to protection against double jeopardy.
Therefore the President of the United States, the State Department of the United States, and indeed the entire government of the United States should refuse any extradition request for Amanda Knox to return to Italy to serve any form of incarceration.