Blachford, Theodosia (1744–1817?), philanthropist and leading methodist, was born at her father's residence in Rosanna, Co. Wicklow, only daughter of William Tighe (qv), landowner and MP, and Lady Mary Tighe of Rathmore, Co. Meath, eldest daughter of John Bligh, 1st earl of Darnley. She was left motherless from early childhood; her father later married the heiress Margaret Theaker, with whom he had a son and daughter. Theodosia initially had a troubled relationship with the second Mrs Tighe, but in time became close to her stepmother. A reflective and intelligent child, she read extensively from a young age and to a great degree educated herself. After receiving a conventional religious upbringing in the Church of Ireland, she experienced a form of spiritual awakening at the age of 17, after which she read widely on religious matters and resolved to ‘renounce the world’. She married (1770) the Rev. William Blachford, prebendary to Tassasagart, who served as librarian to St Patrick's and the Marsh libraries in Dublin. He died in May 1773, leaving her to care for their two children, the younger of whom was the poet Mary Tighe (qv), whose education she saw to personally. She converted to methodism c.1775, possibly as a result of her bereavement or through the influence of Agnes Smyth. Attached to the Whitefriar St. church, Blachford with her aristocratic connections was inevitably a conspicuous figure in Dublin methodist circles, and by June 1788 she appears in John Wesley's correspondence, described as ‘one of our jewels’. She wrote several religious tracts and produced a translation of the life of Jeanne de Chantal, founder of the Visitation Order. Her sister-in-law Sarah Tighe (1743–1820), a supporter of charities in her native Co. Kilkenny, similarly converted to methodism.
Despite her relative wealth, she lived frugally and gave much of her surplus income to charity. A benefactor of the Magadalen Asylum on Leeson St., Dublin, she played a leading role in the establishment of the Female Orphan House (1790) and the House of Refuge on Baggot St. (1802), founded to assist homeless and unemployed young women. Crookshank also refers to her personally educating a number of impoverished girls. She evidently found this work fulfilling and spoke of it as a ‘providential blessing’ which ‘saves me from stupid indolence’. It may have served as a distraction from her personal anxieties. She disapproved of her daughter's marriage to her cousin Henry Tighe, and despaired of what she considered her frivolous lifestyle, yet spent much of her time in England with her. Having nursed her daughter through a lengthy illness and eventual death (1810), she only briefly survived her son John, who died in the summer of 1817.