Sisters of Sword and Shadow by Bates Laura

What if the Knights of the Round Table had been women?

This afternoon Cass's older sister will be married. Soon she will be too. Gone will be days of running through fields and feeling the earth between her toes. So when a beautiful leather-clad woman rides up and offers to take her away, Cass doesn't hesitate to join her.

Cass is introduced to the Sisterhood of Silk Knights - a group of women training to fight and working to right the wrongs of men. Cass is drawn into a world of ancient feuds, glorious battles, and deadly intrigue, where soon discovers she holds a power that could change the destiny of her sisterhood.

'An interesting thing happens, when a man is defeated in combat by a woman.'
'He tells nobody.'