Lucy Mansel was born in County Clare, Ireland, probably in 1830 or 1831, the elder daughter of Maria Armstrong and her husband, Lieutenant Colonel Robert Mansel of the 6th (Inniskilling) Dragoons. She was brought up in Hampshire, England, and later lived on the Isle of Wight.
When her brother Robert, a former naval officer, died in South Africa, Lucy, an unmarried woman in her early 50s, decided to emigrate to New Zealand with six nephews: four of her brother's children and two of those of her sister, Mary Dowell, ranging in age from about 12 to 20 years. On 10 December 1883 they departed from London on the Northumberland as part of George Vesey Stewart's fourth group of special settlers. The ship arrived at Auckland in March 1884, and Lucy Mansel and her nephews continued on to the Bay of Plenty by sea.
On 29 April she signed an agreement to purchase the 320-acre Yatton estate, five miles south-west of Tauranga. The land, buildings and equipment were bought from John Alfred Chadwick for £11 11s. 6d. per acre. She received title on 7 August 1884, and immediately began to renovate the homestead and landscape the garden. The original four-roomed house was enlarged until it consisted of eight bedrooms, a drawing room, a dining room with a 16-foot mahogany table, and a kitchen, dairy and outbuildings. A large tapestry depicting St Anthony and St Paul hung in the homestead. Gardeners laid out the grounds with flower- and herb-beds, fruit and nut trees and ornamental shrubs. Box-edged walks led through the Australian exotics, planted by the Chadwicks, which were to become an integral feature of Yatton Park. An avenue of pines led to a courtyard enclosed by the wings of the house. Lucy Mansel ran the farm with her nephews and farm cadets brought out from Britain.
Yatton soon became the focal point of the social and cultural life of the district. A huge barn, constructed out of timber from the barracks of the Gate Pa redoubt, was used for balls and dances. Lucy's success attracted other members of the family to the area, including her sister, Mary Dowell, and brother-in-law, Lieutenant Colonel G. D. Dowell.
Lucy was deeply religious and attended Anglican services in the Greerton School. In 1884 she organised a Sunday school, teaching there for many years. She took an active part in the establishment of a memorial church on the site of the battle of Gate Pa and contributed towards the cost of its construction. She is thought to have been the only woman on the building committee. When Gate Pa Memorial Church (soon afterwards renamed St George's Memorial Church) was built in 1900 she donated a baptismal font. Yatton estate was used for church picnics by all the Tauranga congregations.
Well liked and respected, Lucy Mansel was also admired for taking on the upbringing of a family of boys. She was described by a friend as an angel. She died at Greerton on 22 January 1916 aged 85, and is buried in the Tauranga cemetery.