The History of the Adeptus Sororitas might be a short span considering the Imperium of Mankind in all its glory, but it is deep and fascinating nonetheless. It is one of the main reasons I fell for the Sisters of Battle and gives a much deeper impression of the Imperium of normal man, than the history of the Adeptus Astartes for example.
But it all started long before the Sororitas, with the growing might of the Adeptus Ministorum and the Ecclesiarchy.
If you want to find out more about it and dive deep into the history of the 36th Millenium, I recommend the following Video. Enjoy!