Iowa was one of the few states that had girls bball with teams competing in leagues and playing for a state championship from 1920 on. They played only a 6 player tournament until 1984. The 6 player game hung on for a few more years, but most girls no longer wanted to play it.
I don't know when other states started offering girls bball on a competitive level. Many had offered at least intramural for a long time or AAU ball which parents ran. Many started coming on in the 60s, most went to the 5 player game almost immediately. Some spent some time playing 6 player, but it was soon replaced from what I remember.
Iowa was a late convert to the 5 player game and IIRC Oklahoma was even later. Illinois - right next to us - went right to the 5 player game when they started in the 70s.
One of the death knells for the 6 player game was that Iowa girls, once a prized commodity for the colleges that suddenly were offering women's basketball because of Title 19 were no longer getting the scholarships they once got easily. As other states went to the 5 player, Iowa's girls that played 6 player were lacking in needed skills.
By the 60s most states had HS sports for girls but I am fairly sure Iowa and to some extent Oklahoma were leaders doing it in the 1920s.
I spent many a Friday and Saturday in March in the 50s when I was a kid watching the girl's state tourney games.
BTW - one of the most famous name players ever was once a very good Iowa HS player. Her name was Fonda Dicks from Moravia who as I recall was an all tournament player in the early 70s. I believe she went on to be a successful coach.