[2] Her DSc thesis received worldwide recognition and praise from the eminent glacial geologist Richard Foster Flint and helped recognise the significance of temperature changes in controlling shifts in global and local vegetation zones.

[1][2] Coetzee made several overseas journeys where she studied with various experts in the field of botany, including a three-month period with Gunnar Erdtman, the pioneer of palynology.

[1][2][5][6] Her research in the 1970s and 1980s helped establish the importance of temperature changes in the history of African vegetation during the Quaternary and that ice ages were not wetter there.

[1][2] The research also showed that during the Neogene period global cooling and Antarctic glaciation drove the replacement of subtropical woodlands by fynbos.

[1] On retiring from the Department of Botany at the University of the Free State in 1988, Coetzee moved to Somerset West, Western Cape.