Dr Theo Hall had strong academic and scientific family connections. Her father, Professor Easterfield, was foundation professor of physics and chemistry at Victoria University, Wellington, and later was the first director of the Cawthron Institute, Nelson. Theo's elder sister, the late Dr Helen Deem, was medical director of the Plunket Society and a well known paediatrician.

After qualifying at Otago University, Dunedin, in 1925 Dr Hall was appointed to the staff of Wellington Hospital as 'house surgeon'. At that time there were very few woman doctors and no accommodation suitable for them at the Wellington Hospital; in view of this Dr Hall occupied herself with locum duties while suitable accommodation was being built. Following her duties on the house staff of Wellington Hospital, she was appointed to Cook Hospital, Gisborne. Sometime thereafter she married the superintendent of the Hospital, Dr RJB Hall, a general surgeon.

She was admitted to membership of the Royal College of Physicians of London in 1932 and returned to Gisborne where she took up the position of specialist physician at Cook Hospital, a post she held until her retirement early in 1958. At the time of the founding of the Royal Australasian College of Physicians in 1938 Dr Hall was in Britain engaged in postgraduate study. She was thus passed over for Foundation Fellowship much to her regret. Her professional duties in Gisborne together with her family responsibilities precluded her taking the membership examination.

The post of physician at Gisborne in the 1940s and 50s was arduous. There were no colleagues of similar seniority and experience, the district was isolated and attendance at clinical meetings difficult in the absence of suitable locum staff. Apart from a quarterly visit from the tuberculosis officer based in Napier, Dr Theo had the responsibility for all of the internal medicine and paediatrics for the district. She carried this burden remarkably well and found time for her reading and the continuing education of those young doctors fortunate enough to work with her.

When her husband Dr RJB Hall retired from the hospital service to live at Paihia, Bay of Islands, Dr Theo took up a post as visiting physician at the Hospital at Kawakawa, a small Northland town near the Bay of Islands. She continued her refreshment by visits to Auckland Hospital to attend grand rounds. She retired from medicine in 1971 due mainly to declining health. She died on 19 December 1980, her husband survived her by a few years. Three daughters live in New Zealand, Mrs Elizabeth Couper, Mrs Dinah Parr and Mrs Angela Cook.