If you are looking for gluten free ice cream in Buenos Aires then Freddo is one good place to go. There have a number of locations throughout the city and clearly label which of their menu items are gluten free.
We ate at the Freddo in Recoleta right across from the city’s famous and very interesting cemetery (where Eva Peron and many others are buried) but I have seen many others in various areas throughout this huge city. A small tub of ice cream was $13 pesos (US $3) so not cheap but not bad. The ice cream tastes really good and you can choose from around 10 different gluten free flavours. I hear that they also do flourless gluten free cake here so I may have to check this out on my next visit.
Other than obvious glutenous ingredients such as cookies, I have no idea what some places put in their ice cream to make it not gluten free! Still, lucky for coeliacs, Freddo have decided to tell us which of their products we can and cannot eat and this makes me very happy.