[4] Ngugi studied at Columbia Pacific University for her BA and Masters in Nursing Administration from 1983 to 1985, and earned a PhD in social work in 1989.

[5][6] In 1986 she became a lecturer in the University of Nairobi, School of Public Health and was eventually promoted to the position of Kenyan national AIDS coordinator.

[2][6] Ngugi was involved in an international collaboration in Nairobi to engage with sex workers and help them to tackle sexual transmitted diseases.

[6][7] Much of Ngugi's research focused on these vulnerable communities, and she provided them with medical care, advice and free condoms in return for participation.

[10] Ngugi and Frank Plummer from Manitoba published a study indicating levels of long-lived HIV resistance among Kenyan sex workers who work in Majengo, Nairobi.

[2] She also led the implementation of government efforts against HIV/AIDS including the building of ten drop-in centres for vulnerable populations in northern and eastern Kenya.