The original alleged offence was committed on board an American registered aircraft. Unless things have changed, that aircraft is the sovereign territory of the United States, and therefore outside the jurisdiction of the Brazilian authorities. Discipline on board is vested in the Captain, via various Air Navigation Acts, and delegated to the crew. Normal procedure would be for the Captain to request security personnel to meet the aircraft and take the alleged perpetrator into custody. The crew can give statements to the local authorities without leaving the sanctity of US sovereign territory.
Unless the Air Marshalls manhandled the lady on Brazilian territory, I do not think there is a case to answer.
Perhaps Flying Lawyer could give us the benefit of his counsel?