Maire o Ciaragain led Irish clans in revolt around 1400.
Queen Margaret of Denmark (1353-1411) led her armies against Swedish and Norwegian forces.
From "Treasure of the City of Ladies" (1405) by Christine de Pizan : "We have also said that she [the baroness] ought to have the heart of a man, that is, she ought to know how to use weapons and be familiar with everything that pertains to them, so that she may be ready to command her men if the need arises. She should know how to launch an attack or to defend against one." (info given by Wendy)
Defenders of a bulwark in Prague in July 1420 included two women and one girl who threw stones and lances at the attacking army. (source "John Zizka and the Hussite Revolution" - Heymann, Frederick G.- Princeton University Press. Info given by Peter Nyikos firstname.lastname@example.org )
Jacqueline of Bavaria, Countess of Holland, Hainault and Zealand (1402-1437) led her army to relieve a seige at the city of Gorkum.
During the siege of Orléans, France, in 1428, townswomen hauled buckets of boiling water, fat, lime and ashes to be poured them down on the English attackers. (source Military History - April 1998 - The Maid of Orléans)
Isabella of Lorraine led an army to free her husband Rene, Duke of Anjou from the Duke of Burgundy in 1429.
Jehanne la Pucelle (Joan of Arc) 1412 - 1431 fought against the English in France.
Margret Paston took charge of the defence of her home in her husband's absence both before and during the Wars of the Roses. She asked him to send crossbows, poleaxes and iron spikes as well as more domestic items in a letter in 1448. (see also: Paston Letters)
Isabella I of Castile (1451-1504) was married to Ferdinand of Aragon. She was heir to her half brother Henry IV of Castille and inherited his throne in her own right in 1474. This led to a war with supporters of his wife's allegedly illegitimate daughter, Juana. Later in her reign she and Ferdinand attacked the Moors and drove them out of Southern Spain. Isabella wore armour and led her army in the field, she also planned strategy and organised the supplies and field hospitals. Her importance to the army was illustrated by the fact that her illness after a miscarriage while she was in command of an army at Toledo in 1475 gave her enemies a respite.
Margaret of Anjou (1430-1482) was a leader of the Lancastrian forces during the War of the Roses. Her armies defeated the Duke of York and the Earl of Warwick.