Marini and her identical twin sister Muriel studied music at the University of Auckland before training at Auckland Hospital to become registered nurses in 1928. During the Second World War they joined the New Zealand Army Nursing Service in 1940 and served until 1945. Marini was posted to Pinewood Hospital in England for three months, treating soldiers sent home to recuperate. She then worked as a Theatre Sister in front-line tent hospitals in Egypt, Greece and Italy and was present during the evacuation form Greece to Crete. Subsequently she became Matron of No 3 NZ General Hospital, Middle East Forces. Both sisters received the Royal Red Cross medal for their war service and had notable nursing careers in Auckland after the war. On her return from the war, Marini became Matron of Greenlane Hospital until her retirement in 1955.

Marini is quoted in the Auckland War Memorial Museum exhibit 'Scars on the Heart' '1941, April 25: Truck capsized with 19 of us. Also air attacks and land bombed. Most uncomfortable. Spent most of the day 12 miles from port in a cemetery until dark when we went in an ambulance to port.'- Marini Jackson, recording her escape from Greece. Items from the sisters' service overseas are also on exhibit: medals, badges, diaries and snapshots. AWMM