Gecaga was born to a Kikuyu family in Kenya. Her parents, Leah Magana and George Segeni Njoroge, were Christian converts who attended the Church of the Torch which had been founded by the famous Church of Scotland minister, John William Arthur. Her father worked as a cook at a Presbyterian mission in Nairobi and later opened a store. She has five brothers and one sister including Kenyan Cabinet Minister and Member of Parliament Njoroge Mungai (1926–2014) and Kenyan diplomat Ngethe Njoroge (formerly married to American activist Mary Morello and father of American guitarist Tom Morello). Her cousin, Jomo Kenyatta, was the first elected president in Kenya.
