Isabella Foster Rogers Kells was born at East Tamaki, New Zealand, on 15 April 1861, the fifth child of Eliza Forbes and her husband, George Kells. Eliza was the daughter of Robert and Margaret Forbes, the first Scottish Presbyterian settlers in Onehunga; George, an Irishman, arrived with the 65th Regiment of Foot in 1846, purchasing a farm at Pakuranga after his discharge from service. The children were educated in Panmure and Onehunga and attended the St Matthias Anglican Sunday school.
Isabella Kells was probably a pupil-teacher before being appointed the head female teacher at Panmure School in 1878. She held this position, at a salary of £50 and later £60 per year, until 1888. In 1889 Kells accepted the invitation of her uncle, F. D. Rich, to take sole charge of a school at Lichfield, a rural locality south-east of Hamilton. Rich was manager of the New Zealand Thames Valley Land Company which had established a state-assisted private school on their new development block at Lichfield in 1884.
The Lichfield school had an average attendance over many years of between 10 and 20 pupils. Kells's teaching methods were conventional and she ensured that her pupils had a thorough grounding in arithmetic, reading, spelling and dictation. Occasionally she varied the routine and took her class to picnic at the Ngutuwera waterfall or to visit Rotorua. The first few years in Lichfield were pleasant and Isabella recalled later the manager's elegant homestead, pheasant shooting parties, tennis parties, lantern picture evenings and all-night dances. However, disastrous falls in prices for bullocks and sheep, and stock losses (later found to be due to trace element deficiencies in the local soils) caused the Thames Valley Land Company to go into liquidation in 1891.
Isabella Kells remained at Lichfield School, but, probably because of a general teacher surplus, her annual salary was reduced to £44 and fluctuated throughout the 1890s. For an additional salary of £13 per annum in 1897 she took charge of the Lichfield post and telegraph office, which was moved to a lean-to attached to the school building. Isabella Kells also took into her home as boarders local children who lived too far away to ride their horses to school daily. After a family tragedy in 1912 her two nephews also came to live with her. One of these boys, Ron, became the well-known poet R. A. K. Mason. She retired from teaching in 1913; however, she was to remain postmistress for another 13 years.
During the First World War Isabella Kells assumed a key role in the community as the bearer of news. She sat in the little telegraph office knitting soldiers' socks as she waited for telegrams from the War Office, which she would then deliver personally, often walking miles in the dark and wet on muddy tracks. Locals congregated by day at the school waiting for Isabella to sort the mail. Her dedication to her duty during those years endeared her to the Lichfield community.
In 1921 a telephone switchboard was wired to the post office. Isabella was paid one pound per year by each of the 25 subscribers for connecting their calls. She finally retired as postmistress in 1926 owing to ill health. In total, she had spent 48 years in the public service, mostly while living at Lichfield. At the retirement dinner given in her honour it was stated that the people of Lichfield had always relied on Isabella Kells, and that 'she had stood like a rock to Lichfield'.
Isabella Kells never married and lived the rest of her life at Lichfield. She was a faithful Anglican, continuing her practice of providing meals for visiting clergy and setting out the local hall with candlesticks and lectern for Sunday services. She died at her home on 12 July 1938 and was buried in Putaruru. In 1961 Chebsey Street at Lichfield was renamed Kells Lane in her honour.