The plaque honoured Women's War Service Auxiliary nurse Private Frances Anderson, who attended the school in 1932 and 1933.
Pte Anderson died in Egypt in 1942, after contracting typhoid, possibly from a failed vaccination.
She joined the Red Cross Society in 1939 and after passing all her voluntary aid examinations, left New Zealand with a detachment of Red Cross and St John Nurses.
She arrived in Egypt in February 1942. In March, family received notification she was seriously ill. She died in Helmich hospital on April 19.
Pte Anderson, one of four children in her family to serve in World War 2, was buried in the Heliopolis War Cemetery.
Her brother, Ivan, was an RAF crewman who delivered a Wellington bomber to the 8th Army just after Miss Anderson (and sister Lucy, also a nurse) arrived in Egypt.
The three spent several days together before Ivan returned to England.
On returning to his squadron, Ivan was handed a brief telegram informing him of Frances' death.
Ivan died, aged 80, of emphysema, which he believed was related to inhaling cordite fumes while serving as a tail-gunner in RAF bombers.
Brian Anderson, formerly of Dunedin and now of Christchurch, and several family members from Otago attended yesterday's assembly. Mr Anderson remembers his "vivacious'' aunts (Frances and Lucy), whom he met as a 3-year-old just before they left for war.
"I remember laughter and kindness, and them making a great fuss of me as a young boy," he said.
"We are just so pleased the school has chosen to acknowledge her sacrifice,'' he said.
Miss Anderson's sister, Lucy Fowler, now aged 91, lives in Christchurch.
The plaque will be displayed in the Dalrymple Building Otago Girls High School principal Jan Anderson said.
An award-winning short film by Otago Girls pupils Hannah Port, Mei Mackay, Elena Piere and Courtney Simpson (all 17) entitled The Women's War was shown at yesterday's assembly. An article on the pupils' film will follow.
