Barbara Eckersley, 69, faced trial in the NSW Supreme Court this month, charged with murdering her mother at an aged-care centre in August 2018.

Her mother was renowned environmental scientist and botanist Dr Mary White, formerly of Johns River, south of Port Macquarie.

The court heard Eckersley placed the drug known as "green dream" into her food on the day of her death.

Eckersley denied killing her mother, who had severe dementia and other health conditions, Australian Associated Press reported at the start of the trial earlier this month.

A jury handed down its verdict on April 29.

Eckersley was found not guilty of murder, but guilty of manslaughter.

Justice Beech-Jones will be hearing sentencing submissions tomorrow (April 30). The court confirmed sentencing is likely to take place on May 20, 2021.

Ms White, 92, moved to the care home at Bundanoon, in the NSW Southern Highlands, after suffering a stroke in 2016.

She was paralysed on the right side of her body, was incontinent, non-verbal and needed full-time care.

Eckersley planned to move Ms White to a nursing home at Coffs Harbour on August 7 where she would be closer to family. She died two days prior, when Eckersley and her husband Richard were visiting.

Mr Eckersley told the court he was shocked when his wife revealed she had put a drug into her mother's food on the day she died, according to AAP.

After informing detectives of this fact, Eckersley was told she would be charged with murder.

Her lawyer Kieran Ginges said Eckersley would dispute the drugs were the significant cause of Ms White's death. She had a range of health problems including a heart condition and thrombosis.

The court heard earlier this month that Eckersley was severely depressed in August 2018 and did not have the capacity to understand the events.

Evidence presented to the court said Eckersley had the drugs left over from her time working as a wildlife carer in Canberra about two decades earlier, the court was told. It was used to euthanise native animals.

The court heard she added a small amount to her mother's food thinking she would go to sleep, not that it would kill her, Mr Ginges said.

Dr Mary White was born in South Africa and raised in Southern Rhodesia (now Zimbabwe), fascinated by nature since childhood.

She attended the University of Cape Town, where she received a Master's degree in paleobotany - plant fossils and prehistory.

Her lifelong interest in the plant life of Africa meant she travelled extensively through the wild with her husband and young children.

She moved with her family to Australia with her husband in 1955, and until the 1980s, she worked as a consultant to the Bureau of Mineral Resources in Canberra, reporting on field collections of plant fossils.

She also worked part-time as a consultant to mining companies, and as a research associate to the Australian Museum, where she curated the plant fossil collections.

She eventually became a full-time writer and lecturer, publishing several award-winning books on climate change, among them After the Greening: The Browning of Australia, which received a Eureka Prize in 1994.

In 2009, she was award the OAM "for service to botany as a researcher and through the promotion of increased understanding and awareness of the natural world".

She also received a Lifetime Conservation Award from the Australian Geographic Society in 2010, two honorary degrees, and the Riversleigh medal for services to Australian paleontology.

Throughout her latter career, she published numerous books and papers.

Dr White was the patron of Climate Change Australia - Hastings Branch from 2007 to about 2014.

In 2003 she bought a property at Johns River where she established a covenant on the land to maintain biodiversity.

She also developed it as an education centre, welcoming groups who wanted to learn more about the natural environment and how to protect it.

She sold the property in 2013, and had been living in Bundanoon ever since.

Dr White was also a patron of Sustainable Population Australia, an advocacy group for a sustainable Australian population.

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