Immigration

My wife is a US green card holder but moved legally to Canada to take care of our soon who has some health issues.Last year on a trip to Buffalo from canada she was stop by US customs and she was given the options of voluntarily giving up her green card or go to immigration court. Beacause it was a shock to us we decided to go to court but after considering that she might not move back in the near future because of the health of our son we decided to give up the green card status . We gave up the green card at the embassy here IN Canada 8 weeks before the court date but we still got a letter saying a judgment of removal . My concerns are that she gave up the green card already and already left the USA and by giving up the green card she couldnt enter the US even to attend the court date or speak to the counsel about the fact that she gave up her green card already. what do you advise?