Zero extradition. U.S. won't on any grounds or trials that are unconstitutional. This one being simple double-jeopardy.
I feel bad for Kercher's family, but frankly, the kangaroo court third world freakshow that is "Italian Justice", the alternately three stooges then abusive police, and incompetent amateur-hour mistakes in basic scientific procedure and chain of custody in evidence by the forensics people is the much larger issue now. Italy's criminal justice system is an embarrassment to Italy, Europe, and Western Civ in general.
Even if she did do it, Italy essentially went to court with what amounts to a frame job to convict her.
I wouldn't turn *expletive deleted*ing Charles Manson over to them.