Dewes spent her early years living on the East Cape and Bay of Plenty where she consistently heard the te reo Māori language.
Despite learning French, German, Italian and Latin at high school, Dewes was told by the principal that she was not allowed to study Māori.
Dewes was a founding member of the Kura Kaupapa Māori schools movement in New Zealand.
[5] In 1985, Dewes established Te Kura Kaupapa Māori o Ruamata in Rotorua, one of New Zealand's first Maori language schools.
[6] In the 2011 Queen's Birthday Honours, she was appointed an Officer of the New Zealand Order of Merit, for services to Māori.