Who is the earliest 20th century female figure elected to a position as PM or President of a country. Mainly i guess Europe or South America would be the main places I'm curious in since they seem culturally similar to the US. And what was differently socially that enabled women in these countries to hold these offices as compared to the US? Could having female queens have affected their acceptance of female PM's/Presidents?
That would be either Margaret Thatcher 1979 as Prime Minister of the UK or if you want to include Israel Golda Meir in 1969 also as Prime Minister. But both are cases of a parliamentary system not a presidential system as in the US, so both weren't voted for as directly as the US president is (even though the US president is in principle voted in by the electoral college). In these systems the head of government is voted for by the parliament so for the voters the party of the candidates may be more important than the person ending up with the job. In the case of Golda Meir, she was chosen by the majority party after the former prime minister died in office, so she never was part of the election process which ultimately led to her premiership. Thatcher on the other hand was the leader of the conservatives since 1975 before her election as premier, having served as leader of the opposition in the previous legislative period, and so was the face of her party during the campaign and the public already knew her for quite a time. At that time second wave feminism was already under way, in the UK it culminated e.g. in the Equal Pay Act of 1970 and the Sex Discrimination Act of 1975; but it's important to note that Thatcher herself mostly isn't viewed as a feminist herself.
The first democratically elected female head of state was Vigdís Finnbogadóttir 1980 as President of Iceland (a role not comparable with the US presidency).