You have it pretty much summed up. First there is passport control - there are 3 lines - Argentinos, Mercosur, and the rest of the world. Afterward, one goes to the baggage claim, and then through the customs line. All inbound luggage is X-rayed @ customs. There are free baggage carts near the carousels, which may be helpful - grab one before the luggage arrives.

The area just outside customs gets a bit chaotic, so you might want to ask what kind of sign the representative will be holding.

If she is carrying much of value that is not used, she might want to have the receipts to prove she's not "over limit." This is generally of concern with new electronics.