Born on 2 February 1754, she was the daughter of an Otley surgeon, John Ritchie of Edinburgh, who had been a naval surgeon. As a girl, she came under the influence of John Wesley, who often stayed at her home, and became a class leader in the Otley society. In the 1780s she accompanied him on some of his journeys and they corresponded frequently. From 1771 she kept an intimate diary. She was living in Wesley's London house during the last months of his life and became close friends with Hester Ann Rogers. She was present at his death in 1791 and at the request of John Whitehead wrote an account of his last days. She was encouraged by Mary Bosanquet to undertake evangelical and philanthropic activities. In 1801 she married a former suitor, Harvey Walklake Mortimer, a widower with six children. In spite of poor health when in her twenties, she lived to a good age, dying in Islington on 9 April 1835. She is buried in the crypt at Wesley's Chapel.