A former security guard left severely traumatised by the deadly riots at the Manus Island detention centre has taken her own life before her legal battle with the Australian government and G4S Australia reaches court - after writing a suicide note addressed to the Prime Minister.

Diane Parker, 53, was one of 18 former staff to pursue compensation through the courts - with the first case to proceed to trial next week.

The Age and The Sydney Morning Herald can reveal Ms Parker pleaded with the government to settle her claim in a hand-written letter addressed to Prime Minister Scott Morrison, who was immigration minister in 2014 when weeks of protests by asylum seekers erupted into three days of violence.

"Scott Morrison, My name is Diane Parker, I was working on Manus Island in Papua New Guinea in February 2014. Do I need to go on?

"I have PTSD and have committed suicide. I am over the courts, over the delay, over people not caring," Ms Parker said in the letter on June 27, 2019.