The former foreign minister of the regime, who is 87, has spent an extensive amount of time in the hospital since September.
The civil party structure is meant to add some public reconciliation to the process, a major mandate of the court.
Her release angered many victims of the Khmer Rouge, who fear she is trying to avoid being brought to justice for crimes committed by the Khmer Rouge under leadership.
Ieng Sary, who is 88, is on trial for atrocity crimes alongside top leaders Nuon Chea and Khieu Samphan.
Ieng Sary, 87, has been in the hospital since Sept. 7 and has been unable to participate in hearings since.
One aim of the visit is to put data from the UN-backed Khmer Rouge tribunal into a exhibition at the Holocaust museum in Washington.
Pouch Kri said he is disappointed because one thing Sihanouk never did was clarify his role in the rise of the Khmer Rouge before the UN-backed tribunal underway in Phnom Penh.
Cambodians living in the US and suffering from the trauma of the Khmer Rouge might in fact be physically unhealthy as a result.
The delegation will be examining the UN-backed atrocity crimes tribunal, visiting the “killing fields” of the country, and learning what challenges the country still faces in coming to terms with its past.
Former king Norodom Sihanouk's most lasting legacy was the winning of independence for his country from colonial France in 1953.
Some 16,000 people were tortured and subsequently executed at the prison, known to the Khmer Rouge as S-21,
Tribunal monitors say they hope Harmon’s arrival will mean the two cases will move forward, especially Case 004, which could be wrapped up before Case 003.