When Thomas Reibey died on 5 April 1811, Mary assumed sole responsibility for the care of seven children and the control of numerous business enterprises. She was no stranger to this task, having managed her husband's affairs during his frequent absences from Sydney. Now a woman of considerable wealth by her husband's businesses, Reibey continued to expand her business interests. In 1812 she opened a new warehouse in George Street and in 1817 extended her shipping operations with the purchase of further vessels. In the same year, the Bank of New South Wales was founded in her house in Macquarie Place.