What historically significant happenings were impacting female writers at the time 1865-1912?
I'm assuming you mean American writers. Correct me if I am wrong and I'll modify my response. It's tough to gauge the actual impact of events on female writers, but it was a very important time frame for women.
Women were politically active in the temperance (anti-alcohol) movement beginning with the Women's Christian Temperance Movement and later the Anti-Saloon League. This was empowering for them as they stepped onto the national political scene. They were also active in women's suffrage, and many states, starting with Wyoming in 1867, legalized women's voting before the Constitution was changed.
Women were increasingly gaining access to education at the high school level, and were a large part of the garment industry's workforce. They were active in reform of working conditions as well, especially in the years leading up to and following the Triangle Shirtwaist Fire (at the end of your time frame).