Greensill is of
Tainui,
Ngāti Porou, and Ngāti Paniora descent, born in the late 1940s in
Hamilton and raised at
Raglan, on the
turangawaewae of Tainui o Tainui ki Whaingaroa. She was educated at Raglan Primary, Raglan District High School, Hamilton Technical College, Hamilton Teachers College and at Waikato University. She holds a Trained Teachers Certificate, LLB (Bachelor of Laws), Bachelor of Social Sciences with 1st class Honours and completed a Masters of Social Science in 2010, with a thesis on the
Resource Management Act, supervised by
Robyn Longhurst. Greensill's first job was as a primary school teacher both in New Zealand and in
Brisbane. Between 1984–1996 while raising her young family, she worked for her
hapū as co-ordinator of employment and skills training and conservation programmes for youth in the Raglan Catchment area. After completing a law degree she was employed by
University of Waikato in 1999 to teach in the Department of Geography, Tourism and Environmental Planning specialising in treaties, Māori geography and resource management. ==The environment==