Coba Ritsema was one of the few female artists of her time. She became known for her still lifes, portraits, and interiors in an impressionist style that suited the prevailing taste of the time at the beginning of the 20th century. Her compositions, initially somber, became increasingly free over the years, her colours lighter and fresher, and her brushstrokes broader, almost masculine and instantly recognizable. More and more women in that period were given the opportunity to become proficient in painting and, like Ritsema, were admitted to the 'women's class' of August Allebé at the Rijksacademie, where they were taught by Nicolaas van der Waay and Carel Dake. The class also included Marie van Regteren Altena, Jo Bauer-Stumpff, and Lizzy Assingh. With them and a few other female artist friends, Ritsema founded an artists' association, which art critic Albert Plasschaert introduced in 1912 as the 'Amsterdamse Joffers' (Amsterdam Women's Association). The group contributed significantly to the acceptance of women in art at the time, meeting weekly to paint and also exhibiting together. Meanwhile, Ritsema rented a studio in Haarlem, where she also received landscape painting lessons for two years from her brother Jacob, with whom she traveled to the Gooi region. In 1899, she moved to Amsterdam, where her studio was located at Singel 512.
Ritsema was a gifted painter who received national and international recognition. Among other awards, she received the Willink van Collen Prize in 1900, the bronze medal at the Brussels World Exhibition in 1910, and the Royal Arti Medal, presented by Queen Wilhelmina, in 1918. She remained active well into old age in her fourth-floor studio, which she still climbed herself and where she had placed a chair on each floor for rest due to a heart condition. Her work always sold well, and her subjects, combined with her powerful brushwork and vibrant use of colour, were popular. Yet, throughout her life, she remained insecure about her work, which she found difficult to give up and which she always felt could be improved.