By 1566, Ní Mháille had married a second time, this time to Risdeárd an Iarainn ("Iron Richard") Bourke, his nickname deriving from his ironworks at Burrishoole, the place of his principal castle and residence. The 1st Viscount Mayo was a child of this marriage.
Still not satisfied with her revenge, Ní Mháille then sailed for Ballycroy and attacked the garrison at Doona Castle, overpowering the defenders and taking the castle for herself. Her attack against the MacMahons was not the first time she interrupted someone at their prayers. Legend tells of another lord who stole property from her and fled to a church for sanctuary. She was determined to wait out the thief, maintaining that he could starve or surrender. The thief dug a tunnel and escaped, however, and the hermit who took care of the church broke his vow of silence to scold her for attempting to harm someone who had sought sanctuary. Her reply is not recorded.
In the later 16th-century, English power steadily increased in Ireland and Ní Mháille's power was steadily encroached upon. Finally in 1593, when her family (her two sons Tibbot Burke and Murrough O'Flaherty, and her half-brother Dónal na Píopa) were taken captive by the English governor of Connacht, Sir Richard Bingham, Ní Mháille sailed to England to petition Queen Elizabeth I for their release. Elizabeth I famously sent Ní Mháille a list of questions, which were answered and returned to Elizabeth. Ní Mháille then met with the Queen at Greenwich Palace, wearing a fine gown, the two of them were surrounded by guards and the members of Elizabeth's royal Court. Ní Mháille refused to bow before Elizabeth because she didn't recognise her as the "Queen of Ireland."