Further surfing on the subject of women in armor has taken me inevitably to more sites associated with SCA (The Society for Creative Anachronism). SwordMaiden.com is one such, and has among other interesting information, a page about women fighters in history. It contains these anecdotes, which I pass on to you:
In the 14th century, Sir Richard Shaw wrote of fighting and besting a Flemish knight who, when the armor was opened, turned out to be a woman whose identity was never discovered.
Agnes Hotot of House Dudley (born approximately 1378AD) took up arms in the place of her ailing father and bested her opponent in a mounted duel. The family coat of arms show a woman in a helmet, hair disheveled and breasts exposed (apparently she exposed them after the duel to humiliate her opponent).
Pierre Gentien, a French poet of the 13th century, wrote a rhymed epic in which he names some 50 women who, in order to prepare for the Crusades, held and participated in a tournament.
The songs and tales of the time are replete with tales of unknown knights who enter tournaments. Could some of them have been women in disguise?