Tango,
If you mean ladies like Bradamante in Ariosto's Orlando Furioso or Britomart in Spencer's Fairie Queen who aspired to knighthood, went through the weapons training, and the whole page-squire-knighted after a night of vigil in the chapel thing, then went forth to engage in acts of knight errantry, basically, no.
Ladies could inherit knights' fees if there were no male heirs. I suspect most of them would have hired a professional warrior as a stand in when the king called them up for duty with his army.
There were ladies, like Sichelgaita, wife of Robert Guiscard, who lead armies, carried arms, wore armor, and sometimes fought.
When Tortosa, in Catalonia was attacked by Moors, the ladies of the town helped defend it. The feudal overlord, the Count of Barcelona, established a knightly order to honor these ladies, known as the Order of the Hatchet.
I found this on the internet: link
Grelber
gets medieval.
