She was a daughter of John Cobela Ntuli and his wife, and was born at Mapumulo Mission Station (between Stanger and Kranskop), Natal, probably between 1885 and 1895. (Mangena apparently used her father's name for a surname. In all her correspondence she is referred to as 'Victoria Cobela'.)
Mangena received her schooling at the Inanda Seminary (or Lindley's Seminary). Instead of following the teaching profession which was about the only profession open to African youths at the time, she decided to become a nurse. She went to one of the few hospitals that did train Africans as nurses Victoria Hospital, Lovedale in the Eastern Cape. She received her training under Dr Neil Macvicar* who was encouraging young African women to be trained as nurses.
As soon as she had qualified in 1910, she came to the Transvaal where she worked at a number of places as the first qualified African nurse. At Klerksdorp Hospital she worked for two years under Matron Helen Scott Russell as so called 'native nurse'. At the end of June 1915 she left Klerksdorp and joined the staff of the Crown Mines Native Hospital in Johannesburg, working under Matron T. Silverman. She remained there for six months. Apparently she also did some private nursing besides her work at the hospital.
During the Great Influenza Epidemic of 1918, while she was still in Pretoria, Mangena heard that the New Brighton Location Hospital in Port Elizabeth was understaffed. She applied for a vacancy as a nurse at New Brighton and assumed duties on 1 November 1920. Mangena was mainly responsible for district nursing while her colleague Dora Jacobs worked in the hospital. When the latter left in 1923 Mangena took charge of the hospital services.
After her husband's death in 1924 Mangena returned to Johannesburg and was employed by the city council as a nurse at Klipspruit township, near Johannesburg. She worked for a number of years for the Johannesburg City Council.
She was a leading member of the Wesleyan Methodist Church in Klipspruit, involving herself in community affairs. In her later life she did social service for the Public Utility Transport Corporation (PUTCO).
Mangena died in Klipspruit, Johannesburg, in 1961. It is not known if she had any children.