I may have posted this elsewhere in these pages.
Some time between 1981 and 1986 I was, for my sins, in charge of a junior school football team. It had always been made up entirely of boys. However, there was one particular top year girl who was big, strong and skilled. I selected her for the school team and she played on several occasions. Her name was Simone and that was usefully androgynous when the kids shouted out to each other. I heard the opposing parents asking one another "Is that a girl?" and so far as I am aware they never received a conclusive answer to their question.
The head teacher was a terribly fossilised old git, even by 1980s standards. He brought the matter up with me and I defended my decision strongly. I don't think he had any interest whatever in sport or football, he was just sexist or "traditionalist" as he would have put it. However, he knew me well enough that if he decided to overrule me in this matter, he would have had to find some other mug to run his school football team.
Maybe people who know better than I do (and that is pretty much anyone) can tell me what the FA rules were in the 1980s regarding girls and football. I seem to remember, since leaving full-time teaching, of incidents which, to my mind, have been blown up out of all proportion because somewhere in the rules of football it states that girls were not allowed to play and someone dared contravene that rule. It never came to that in the case I mention above. So far as I know, no-one complained and the issue was never raised.
Edit: I've found this
https://www.theguardian.com/football/2016/sep/03/playing-with-the-boys-womens-football-fa which indicates that even as recenty as 2016 there were major issues with girls and boys playing together.