Known as 'Madam Griffith', daughter of Cadwaladr Wynne of Plas y Foelas, Denbighshire, she married William Griffith of Cefnamwlch, Caernarfonshire early in the 1740s. Converted in 1747, the couple showed an interest in Methodism and in October 1748 she met Howell Harris in North Wales . In 1749, claiming to have separated from her abusive husband, she appeared at Trevecka and began a close friendship with Harris which soon led him to regard her as a prophetess with God-given powers of discernment. She began accompanying him on his preaching tours. Though an uneasy relationship, their friendship caused widespread rumours in Wales and heightened the tension between Harris and Daniel Rowland, which led to the separation within Welsh Calvinistic Methodism in 1750. In Harris's plans for a Christian community at Trevecka early in the 1750s, Griffith was included (rather than Harris's wife) as the 'Mother', while he was to be the 'Father'. Towards the end of 1751 her health deteriorated and following her death from TB in London on 31 May 1752 Harris retired from public life.