U.S. appeals are NOT re-trials, otto. I don't know where you got that idea, but Ms. Mellas certainly knows better.
U.S. appellate courts look at trials to see if they were conducted fairly and according to current trial rules. If errors were made, the appellate court then decides whether the errors rise to a level requiring remedy. (This does not happen often. It's much more common for appellate courts to rule that yes, there was an error, but it wasn't bad enough to overturn the verdict.)
If so, ordering a re-trial is a possible remedy. (In extreme cases such as those featuring obvious corruption, an appellate court can declare a defendant factually innocent, but that almost never happens.) The re-trial is then conducted in the same circuit as the original trial, not in an appellate court.