Throughout history, have there ever been any...?

there were some female rulers who led armies personally. Matilda of Tuscany is a notable example. she was trained in warfare as a Child. she studied martial arts, learnt to fight on horseback with spear and lance, and use the sword, pike and battle axe. She fought at the head of her own armies and led expeditions in aid of the popes. she was particularly close to pope gregory VII.

No, there would not have been female Knights. Look up the Orders of Knighthood and how they were formed. Joan d'Arc was not a Knight.

Elizabeth I put on the armor. To inspire her troops.

But she was a Queen and could pretty much do whatever she wanted.

This very point is discussed in this article, which suggests there were.

http://www.heraldica.org/topics/orders/wom-kn.htm