Looking at the Epilogue Chapter in: Ocean Liners of the Past: Aquitania. I do not see any mention of any visits to Buenos Aires. She is noted as returing from Sydney [Australia] via Rio de Janeiro in 1943.
I found this old Question of did the Aquitania ever call in Buenos Aires. To the best of my knowledge the answer is no as the port was not equipped to handle a liner this size.
Now to go further on this subject the Aquitania did a series of cruises to South America in 1937 and 1938. The Auqitania didn't call in Buenos Aires she called at the port of Montevideo on March 10, 1937 and stayed there until March 15, 1937 with transfer of passengers to Buenos Aires via river steamer. This transfer was included in the cruise rate.