Mandi has been a freelance writer, journalist and trainer since the 1990s. She has edited several niche consumer magazines, written and read news on radio; edited a magazine for a medical profession for more than two decades; written three non-fiction books for young adults; and trained journalists in reporting on science in South Africa and neighbouring countries.

Writing about health and climate change gave her a keen interest in promoting and facilitating effective and ethical science reporting and -journalism as a profession. As a result, she became involved with SASJA (South African Science Journalists Association) and was president of SASJA for several years. In 2017, she was elected onto the board of the WFSJ (World Federation of Science Journalists), and in 2019, she was elected vice-president of WFSJ and chair of its Health Committee. Mandi also serves on the boards of two NGOs: Community-led Animal Welfare and Campaigning for Cancer.