Starting at the age of 19, Letendre studied at the Montreal School of Fine Arts. She developed close friendships with Paul-Émile Borduas and members of the Automatiste group. The 1954 exhibition La matière chante marked a turning point in her career.
Encouraged by Borduas, as well as by the works of Mousseau and Ferron, Letendre began exploring similar motifs in her paintings and exhibited alongside the Automatiste group between 1952 and 1955. In 1955, she participated in the exhibition Espace 1955 at the Montreal Museum of Fine Arts.
Sharing a studio with fellow Automatiste painter and sculptor Ulysse Comtois, Letendre was also featured in a Weekend Magazine article about non-objective painters based in Montreal.