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). In 2017, she was elected onto the board of the WFSJ (World Federation of Science Journalists), and from 2019 to 2023, she served as vice-president of WFSJ. She is now director of the World Conference of Science Journalism which is due to take place in December 2025, in Pretoria. Mandi also serves on the boards of two NGOs: Community-led Animal Welfare and Campaigning for Cancer.