The first trial had been conducted without reference to the pope, indeed it was carried out in defiance of St. Joan's appeal to the head of the Church. Now an appellate court constituted by the pope, after long inquiry and examination of witnesses, reversed and annulled the sentence pronounced by a local tribunal under Cauchon's presidency. The illegality of the former proceedings was made clear... (from the Catholic Encyclopedia)
I am not familiar with the medieval canon law, but it seems likely that ignoring her appeal to the Pope would have made the sentence invalid (for it was indeed illegal). That is why I made the statement that I did.
When the fix is in, no amount of appeal works--as in any autocracy based on dishonesty and political interests that transcend any calls to justice by the individual. Do you think the Pope was opposing Lefebvre? Nonsense. He was opposing what Lefebvre represented. He had been disobeyed by dozens and dozens of prelates before the Archbishop. But none defended the old faith with such vigor. That was what was opposed, nothing else.