Or Grainne Ni Maille in Irish.
Ireland in the sixteenth century was a dangerous place - the English were trying to take over the whole island, as they had been ever since the days of King John, and outside the English sphere of influence there were the warring Irish families, of whom the O'Malleys were one. Grace inherited a large shipping and trading business from her father, and this is where her reputation as a pirate came from. The family took taxes or tolls from local fishermen for the right to fish in their waters, and extended this practice to passing merchant ships.
Her family also had a string of castles along the County Mayo coast, to protect their maritime interests. One of these was known as Cock's Castle - she got it from her first husband, Donal O'Flaherty (Donal of the Battles). There she was besieged by a rival family, the Joyces, who were so impressed with her defence that they renamed the castle Hen's Castle, the name it still has. Later, she also defended the castle successfully against an English attack.
She was deeply involved in the Irish resistance to English conquest, including providing transport for the gallowsglass mercenaries who came from Scotland to fight in the Irish rebellions - to the extent that the English Governor of Connacht, Sir Richard Bingham, said in a letter that "she was nurse to all rebellions in this province for forty years". It was to remove him from office, and to secure the release of her two sons and her half-brother, that she traveled to London, where she met Queen Elizabeth I at Greenwich Palace. As a Queen herself, and because she did not recognise Elizabeth's claim to rule Ireland, Grace refused to bow to Elizabeth when they met. Because they had no other language in common, they conversed in Latin, and Sir Richard was, indeed, recalled to England (though only for a short time).
It was a complicated period - the English held land in the East, around Dublin, which was known as the Pale, where English laws and customs were enforced. Beyond the Pale (which actually was a long fence/ditch at one point) were the Irish families, carrying on much as they had throughout the medieval period, and with a completely different set of laws and customs.
There was also the problem of religion - the English were officially Protestant by this time, apart from a brief period under Queen Mary, but the Irish were Catholic. Like the Scots looking to the Auld Alliance with France for help against the English, the Irish looked to Catholic Spain - without much success. The English also had a policy of creating Plantations - bringing in English and Scottish settlers to live on previously Irish land, who would be loyal to English overlords and laws - which is why Ulster has such a troubled history even now.
Yet, through all of this, Grace O'Malley managed to make a success of her life, holding lands that supported a thousand cattle, her shipping fleet, a string of castles, and the loyalty of her own clan and the O'Flahertys who followed her after her first husband died.