She held out for three years, in loyalty to her King, HM Charles I.
The most important element of having a castle is defence. The primary purpose of the fortifications is to protect those inside of the castle, and to keep people outside. During the Medieval period, sieges occurred across the world in which invading and attacking armies would try to take a castle by force, and some would result in the castle's garrison being starved and forced to surrender. During the English Civil War, many of the castles across England were seen as a symbol of the King's power, and were attacked by Parliamentarians who demanded control of the buildings. After the Civil War they were blown up or slighted, but one lady who defended one of England's greatest castles for 3 years was Lady Mary Bankes. Lady Mary Bankes was married to the Attorney General to King Charles I, and she remained loyal to the King during the Civil War. She owned Corfe Castle, and whilst her husband fought alongside the King she managed to hold off an incredibly brutal and long 3 year siege of Corfe Castle. It was remarkable that she managed to hold the cannon fire so long, and her defence was responsible for the deaths of around 100 enemy soldiers. The castle eventually was surrendered when she was betrayed and tricked, however the enemy were so impress with Lady Mary's defence that they allowed her to keep the keys to Corfe Castle.