Myra Cohen was born at Reefton, Westland, New Zealand, on 12 May 1892, the third and youngest child of Julia Dimant and her husband, Charles Cohen, proprietors of a stationery and fancy-goods business. Her parents were central figures in local community organisations. From 1898 to around 1905 Myra attended Reefton School (upgraded to Reefton District High School in 1902). She won a scholarship for two years' free tuition at Nelson College for Girls; however, being hampered by defective eyesight, she was obliged to forego this opportunity and her desire to become a journalist.
The Cohen family suffered financial setbacks around 1905 with the deterioration of Charles Cohen's health and his losses in gold speculation. Aged 13, Myra became an assistant at a tobacconist's and barber's saloon in Reefton. On weekdays she worked 12 hours, with a half-hour for lunch, except on Wednesdays, when she was granted a half-holiday. On Saturdays she worked a long day. When the town's 17 hotels closed at 11 p.m. many of the patrons – mostly miners – headed for the saloon, where Myra worked into the small hours of the morning. She was escorted home by her brother Percival, and returned on Sunday mornings to scrub and polish the saloon floor, and sterilise the shaving mugs, razors and other equipment. She was then free for the remainder of the day. Her weekly wage was five shillings.
Observant and capable, Myra Cohen soon learnt how to set a razor by watching the barbers at work and trying her hand on willing customers. She was widely advertised by her employer as 'the only lady barber in New Zealand'. Trade increased and Cohen's wages were raised to 12s. 6d. per week, making her a 'high-salaried young lady'. After about three years the long hours of standing took their toll on Cohen's health. She reluctantly resigned, and assisted whenever she could in the family business. The Cohens' financial circumstances eased in 1910 when Percival won a nationwide lottery for the famous 'Honourable Roddy' nugget (weighing 99 ounces and worth £450), found at the Ross Flats goldfields and named after the minister of mines, Roderick McKenzie. The nugget was purchased from Percival by the government and mounted as a coronation gift to King George V.
Myra Cohen's next employment was as a nurse attendant for Reefton dentist Reginald Sheldon, a position she held for several years before the outbreak of the First World War. Among other tasks, she assisted with the application of gas for extractions, and sterilised all surgical implements. For about 10 days every three weeks Cohen travelled with Sheldon through the Buller Gorge in his specially equipped racing sulky to provide dental care at road- and rail-workers' camps and at the homes of isolated settlers. Under makeshift conditions she assisted with dental examinations and made dentures using a kerosene Primus lamp and vulcaniser.
Cohen's ambitions grew, and in 1914 she became a receptionist and nurse attendant for a well-regarded firm of Greymouth dentists. Here she gained further expertise in manufacturing dentures from vulcanite, turning out hundreds with skill and precision. Cohen lived in a guest-house and became actively involved in the social life of the town. During the First World War she participated with enthusiasm in patriotic fund-raising activities organised by Tom Pollard. As a member of Pollard's Pierrot and Pierrette Show, she was a performer in variety shows, comic operas and a highly successful marching team.
Myra Cohen was compelled to resign from her position as dental assistant when she contracted influenza during the epidemic of 1918. It is not known when she left the West Coast. By April 1919 both her parents had died and her sister Kate had taken charge of the family business, which now traded mainly in books. By 1928, after a period spent in the North Island, Myra had established herself as a milliner in Blenheim. She had a 'modest little workroom' and lived at the City Private Hotel. In October 1928 she entertained Charles Kingsford Smith in her workroom, and later watched him depart from nearby Woodbourne aerodrome on his return flight across the Tasman, an event she considered the 'most thrilling incident' of her life. She remained in Blenheim until at least 1934.
In the early 1950s Myra Cohen compiled her reminiscences of life on the West Coast. Without these, little trace of her varied career would remain. Her later life was spent in Wellington, where from around 1943 she lived in Grace Gavin's boarding house at Oriental Bay. Myra Cohen died in Wellington on 16 November 1959. She had never married.