Aileen Aspden died in North Shore Hospital in 2015.
The 83-year-old was admitted because of a relapse of her Crohn's disease.
The Health and Disability Commissioner Anthony Hill said opportunities to "rescue" Ms Aspen, who was losing blood, were not acted on.
Waitematā District Health Board says it's made made changes following death.
The DHB's chief medical officer Andrew Brandt told reporter Sarah Robson says the care Ms Aspden received was not up to their expected standard.