I recall that before the Perron rule, the Argentinian upper class was largely English educated -literally, they went to Oxford and Cambridge and on occasion came back with an English-bien fiancee in tow. So all of the high society, even if they did not always speak English, definitely thought and acted British. Juan Perron, but mostly Evita, of course pushed the old British-raised elite aside and replaced England Nobility Finesse with Argentinian Campesino chick. (You can clearly see this in the evolution of Evita's style over the years)
So what if the English 'way' instead of being discredited during the Perron years and later dictatorships would instead get more democratized and would permeate through all layers of the population. I can imagine that 1) English is pretty universal as a second language and most people, even if they are very poor English speakers could still read and understand any English internet site. 2) there would be a flourishing market for English-written books and Brittish and American movies in their original language. Specialty theatres would perform English plays from Shakespeare to Harold Pinter in their original language. Until 3) the ethnic English or English-speaking minority and their descendants would of course know to speak Spanish, but continue to speak English amongst themselves even after the third and fourth generation. This can have an incubator effect where there would be more immigration from Enflish-speaking countries so that today, a few generations later, you might have a 20% English-speaking minority as per challenge.
Your post actually gave an idea: suppose Peron doesn't meet Eva - let's say she doesn't land a part in the play where they met in OTL. Instead, Peron ends up hooking up and marrying with some upper class girl of British ascend. It doesn't seem far-fetched, as an Army officer involved in politics would frequent those circles.
If we want this ATL Mrs. Peron to get involved in politics, we can simply go the OTL route: Farrel imprisons Peron due Peron's rise in popularity, the unions organize a protest to set him free and they look at someone more charismatic than them to rally the protesters. Enter ATL Mrs. Peron. She would be criticized by the Argentine pseudo-aristocracy because she isn't acting like she should (ie, like a piece of decoration). But this ATL Mrs. Peron is one of them, unlike Eva, so criticism would be limited and she would provide a bridge between Peronism and the conservative upper class.
This in itself could be worth its own TL.
In any case, regarding the English language, while ATL Mrs. Peron would promote British culture simply by being a popular first lady, learning a foreign language isn't as easy as choosing a different haircut. So I think this still needs the English language to be on demand in the job market. And I don't know if that's the case in the pre-globalization days. How much of a required skill is English for jobs between the 1940-1980s?
There were already academies teaching English in Argentina back then, and there were people who learnt the language. But the POD is about popularizing it. How much useful is that beyond certain professions in that time-frame?