"Medieval French had two words, chevaleresse and chevalière, which were used in two ways: one was for the wife of a knight, and this usage goes back to the 14th century. The other was possibly for a female knight. Here is a quote from Ménestrier, a 17th-century writer on chivalry:

It was not always necessary to be the wife of a knight in order to take this title. Sometimes, when some male fiefs were conceded by special privilege to women, they took the rank of chevaleresse, as one sees plainly in Hemricourt where women who were not wives of knights are called chevaleresses."

lady knights :) - [source]