Here's her backstory:

When the Duke of Brittany died without heir in 1341, there were two
rival claimants for the duchy: Charles of Blois and John of Montfort.
John traveled to the court of King Philip VI of France to press his
claim, but Philip —who just happened to be Charles’ nephew—instead
imprisoned him. Rather than capitulate to this act, John’s wife, Joanna of Flanders,
declared their infant son the de facto leader of the Montfort claim and
promptly declared war against the House of Blois. What would become
known as the War of the Breton Succession became a kind of “Cold War”
during a time of supposed truce in the Hundred Years War when Joanna
called upon King Edward III of England to defend her claim. In one of
her many moments of triumph, she was besieged in the two of Hennebont by
the forces of Charles. Touring her fortifications, she saw that the
enemy encampment was ill-defended and so, donning armor and taking arms,
she led a raid that burned the enemy’s tents and supply lines and then
went on to seize another nearby town. For the daring action she is known
as “Jeanne la Flamme,” and it was just one of her many exploits. The
chronicler Jean le Bel declared that she “was indeed a courageous
woman,” and the famed writer Jean Froissart agreed: “she had the heart
of a lion.”
This took a while.
Thanks, and bye!