Molly Cuddihy died on Tuesday at the Queen Elizabeth University Hospital in Glasgow, the BBC reported.
Ms Cuddihy developed septic shock while being treated for a rare cancer at the hospital, an experience she described while giving evidence to the Scottish Hospitals Inquiry.
It is understood that her death this week was reported to prosecutors by a doctor.
NHS Greater Glasgow and Clyde has expressed its “deepest condolences” to Ms Cuddihy’s family.
The Crown Office and Procurator Fiscal Service (COPFS) said her death is being investigated.
A COPFS spokesman said: “The Procurator Fiscal has received a report on the death of a 23-year-old woman in Glasgow on 26 August 2025.
“An investigation into the death is ongoing and significant developments will be shared with the family througho