During World War I, Rennotte trained Red Cross volunteers and during the 1918 influenza pandemic traveled throughout the state of São Paulo providing medical and humanitarian aid. She was awarded the Merit Cross from Prussia for her efforts, which she would donate in 1935 to the Colégio Piracicabano. In 1922 in Rio de Janeiro, she participated in the First International Feminist Congress organized by Federação Brasileira pelo Progresso Feminino, an affiliate of the International Woman Suffrage Alliance. As part of a South American tour, Carrie Chapman Catt attended the Congress and then went to São Paulo with Rennotte to help her found the "Aliança Paulista pelo Sufrágio Feminino" (Paulistan Alliance for Women's Suffrage). Rennotte was elected a vice president of the organization. When 5,000 civilians were injured during the Paulista Revolt of 1924, she set up a hospital ward in Brás in the Teatro Colombo because hospitals were unable to provide enough beds. She continued to be active in scientific conferences, meetings and civic groups until 1935. In 1938, a petition was presented to the Legislative Assembly of São Paulo by journalist Mário Guastini asking for a pension for Rennotte. She was granted a lifetime sum of 1,000 ₢ because of her poverty and infirmity, having lost her sight and hearing.