The Bariloche leg, I believe, took place on 3 Dec. That means that Asuncion, if it takes place today, cannot be Leg 4. If confirmed, it most likely would be the fifth leg. Speculation: fourth leg in Buenos Aires then?
Agreeing with DrRox on the flight Amy was on. If she was in the Asuncion airport headed to Uruguay seven hours ago (it is now 2.30pm in Asuncion), the flight she was taking was probably PU 706 to Montevideo, departing at 9.20am. Asuncion Intl only has one concourse for arriving and departing flights, so it is entirely possible that the crew was waiting for arrivals while Amy was leaving.