The Princess Knight by Cornelia Funke
Plot Summary: Violet is a young princess who wishes she could show the world that she is just as brave and strong as her brothers. But her strict father insists that she get married, and her brothers only mock her when she wants to be included in their fun. So Violet decides to use her intelligence and bravery to show everyone--once and for all--what she's made of. Disguising herself as a boy, Violet takes part in a knights' jousting tournament. When she wins the contest, she reveals her true identity--and wins the prize of freedom!
Youtube link: https://www.youtube.com/watch?v=gafCbfnRbCY
This is a very cute story about a girl who breaks gender norms to fight and ride and eventually beat all the other knights to win her own hand in marriage. Gender bending fantasy stories are very fun, but the lady-knight-avoids-marriage plot has been done many times.