Ina Post was born on 5 August 1941 in
Amsterdam, Netherlands to parents Gerritdina Fransina (née Bruinenberg) and Jan Post; she was their only daughter. Following the end of
World War II the family had moved to South Africa, traveling on the ship
Pretoria Castle in 1949. They had taken residence at
Villieria, a suburb of
Pretoria. Her initial school education was at the Primary School in Sunnyside and the Wonderboom High School. She completed her matriculation in 1959 with the principal of the high school supporting her, even though her mother had desired her to take up a job to run the family. After matriculation, Plug worked as a librarian at the
University of South Africa and concurrently took up further studies at the same university, receiving a BA degree in library science in 1968. At the university, in 1970, she met
Cornelis Plug, a physicist at the Iscor (Iron and Steel Corporation) who later had a successful career in the Department of Psychology at the University of South Africa. She married Cornelis in 1962. They have two children, Ada and Ingrid; Ada is a social worker at the Leeukop Prison,
Johannesburg, and Ingrid works as a librarian at the University of South Africa. Plug then continued her studies in
anthropology and
archaeology at the university. She finished her studies in anthropology up to third-year level, and archaeology to second-year level as at that time the university provided college education in these subjects to that level only. Concurrently, she also studied for an Honours course in the Department of Anthropology (
Volkekunde) in the
University of Pretoria and received her Honours degree cum laude, in 1972. ==Research==