The 83-year-old grandmother made national headlines in December 2008 when she had "DO NOT RESUSCITATE" tattooed on her chest.
The outspoken Dunedin convener of the voluntary euthanasia support group Exit International was a supporter of Sean Davison, who helped his cancer-ridden mother die.
Exit International founder Dr Philip Nitschke praised Ms Westoby for her work concerning euthanasia, and was saddened to hear of her death.
"We had no idea this was going to happen."
The pair had been in regular email contact about going to South Africa to visit Mr Davison, who could not be contacted last night.
"Mum thrived on death ... it was the only thing that kept her going," Jonathan Westoby told the Otago Daily Times yesterday afternoon.
The Auckland-based man was contacted on Monday morning by a Dunedin funeral home to say his mother had telephoned them concerning possible funeral arrangements.
Mr Westoby contacted his Dunedin-based brother, Simon, who found their mother with no signs of life in her Queen St flat, where she lived alone.
St John was called, with staff later confirming her dead at the scene. Police were contacted.
The home was initially treated as a crime scene.
Ms Westoby's death has since been referred to the coroner.
A postmortem is expected today.
The ODT understands Ms Westoby, who had emphysema, undertook a recent fact-finding trip to Argentina, and had a regular trip booked to Rarotonga later this year.
A note detailing some of her final requests indicated she wanted her family to take her ashes to the Captain Cook Tavern while they had a drink, Mr Westoby said.
Fighting back tears, Mr Westoby read a note written last week by his mother which mentioned her love of Handel's Messiah, and how she had considered having a wake with her children before she died.
"Thinking of my ducklings," she wrote in another note, in reference to her five children, two of whom arrived from Australia yesterday.
A service will be held at Gillions Chapel in Dunedin on Friday at 9.30am.
"Mum would want the whole world there. She would. That was the kind of person she was."
