Dr Gill looked after her mother following her father's death in 1999
A woman had mental problems when she made a will leaving her £2.34m estate to the RSPCA rather than her daughter, a court has heard.
Joyce Gill suffered from agoraphobia with panic disorder when she and her husband John made their wills, a High Court hearing in Leeds was told.
An expert said she would have been very anxious when meeting the solicitor.
The couple's daughter, Christine Gill, 58, of Northallerton, North Yorkshire is challenging the will.
The court has heard that Dr Gill - an only child - was given repeated assurances that she would inherit Potto Carr Farm, in North Yorkshire, when her parents died.
The university lecturer told the court she had devoted most of her spare time over a period of more than 30 years to voluntarily helping out at the farm.
When Mr Gill died in 1999, aged 82, Dr Gill was left to look after her mother and run the farm, the court has heard.
It was only when her mother died in 2006, also aged 82, that Dr Gill saw the will, which left everything to the RSPCA.
Rob Howard, a consultant psychiatrist, told the resumed hearing that he had compiled a report about Mrs Gill's mental health based on witness statements and came to the conclusion she suffered from agoraphobia with panic disorder, which began in her childhood.
Professor Howard told the court: "Seeing a solicitor, even with Mr Gill being present, would have been outside the set of situations within which Mrs Gill would have been expected to have been able to prevent the emergence of severe anxiety symptoms.
"My opinion would be that this would be likely to have materially affected her ability to concentrate upon and digest what was being said to her during such a meeting."
The court heard previously that Mr Gill was stubborn and domineering towards his wife, who went everywhere with him and was dependent on him to make decisions for her.
The hearing is due to last until the end of the week, when Judge James Allen QC is expected to reserve his judgment.