Just as others said, any correo argentino works. Stress that you need it with the 'exception of article 51', I even brought a print out of the embassy's packet 3 that explained what we needed.
However All of that and they still got it wrong! But don't worry if You get your police report without the exception, you can file for the correct one online... On the same website that you got your appointment from (http://www.dnrpa.gov.ar). We had to file a complaint on that website that our police report came in without the exception of article 51. The correct form came in within a few days.
Okay great! So she should just find the nearest Correo Argentino to her place and go ask for it in person or via phone/ email? How long did it take them to give it to you?
L+D got a reaction from E&E16 in Argentina and Packet 3