In the mid-1980s, Wanjiku established an independent studio practice in Diani on the Kenyan coast. She made regular journeys from Diani to Nairobi to show her work at Gallery Watatu. Gallery director Ruth Schaffner recognized her talent, hailing her as one of the most important female artists in Kenya. Schaffner mentored Wanjiku and introduced her work to international collections.
Over her four-decade career, Wanjiku participated in exhibitions in Kenya, Uganda, Germany, Japan, and the US. In her later years, she moved to Uganda with her husband, continuing to paint and engage in community work until her passing on January 7, 2021. Today, her paintings are featured in regional auctions—such as Art Auction East Africa—and are preserved in prominent public and private collections.