Zelee's research spans several areas of maternal, child and neonatal health including care seeking, improving the performance of community health workers, behaviour change at community and health-worker level, community newborn care, and early child development. At its core her research focuses on interventions implemented at scale in real life settings, that explore cutting edge issues and that have direct policy implications.

She has significant experience working in Africa (Ethiopia, Ghana, Zambia, South Africa, Tanzania, Uganda, Mozambique, Burkina Faso, Nigeria), Latin America (Brazil, Peru, Ecuador), and Asia (Vietnam, India, Pakistan), and with over 30 institutes.