Tertia was born in South Africa in 1964. She studied Fine Arts at Stellenbosch University. In the first four year degree course she studied under Paul Emsley and majored in Painting and History of Art. In the practical teaching, strong emphasis was placed on disciplined portrait and figure studies as well as still-lives.

From this foundation, Tertia expanded her artistic vision after completing her Baccalaureate in Fine arts in 1987. She continued to study art through a two year Honours Degree. Her paintings were influenced by the 20th-century avant-garde surrealist movement in art and literature which sought to release the creative potential of the unconscious mind, for example by the irrational juxtaposition of images. Dreams play a integral part in her life.

In 1986 she got married to Pierre Kleinhans who obtained a LLB degree at Stellenbosch University during that same time.