Based on her own (Muriel Leo’s nee Oliver, 1917-1998) Family Tree.
Date and place of death confirmed by Rachel Frances Oliver born 31 August 1940

New Zealand Electoral Roll - Wellington North Supplementary Roll No. 1 for 1938, found in June 2018:
Oliver, Muriel Thelma, 8[?] Church Street, spinster

New Zealand Electoral Roll - Wellington West Supplementary Roll No. 1 for 1938, found in June 2018:
Leo, Thomas William, 145a Aro Street, clerk

Brian of nzolivers.com finds it interesting that in 1938 both Muriel Oliver and Thomas Leo were living in Wellington at the same time they were single and wonders is this where they met? The next record of NZ Electoral Roll has them as married by 1946 and still living in Wellington.

New Zealand Electoral Roll - Mount Victoria [Wellington] General Roll for 1946, found in June 2018:
Leo, Muriel Thelma, 7A Elizabeth Street, married
Leo, Thomas William, 7A Elizabeth Street, clerk

New Zealand Electoral Roll - Tamaki General Roll for 1949, found in June 2018:
Leo, Muriel Thelma, 8 Te Arawa St., SE2. married
Leo, Thomas William, 8 Te Arawa St., SE2. civil servant

New Zealand Electoral Roll - Tamaki General Roll for 1954, found in June 2018:
Leo, Muriel Thelma, 8 Te Arawa St., SE2. married
Leo, Thomas William, 8 Te Arawa St., SE2. civil servant

New Zealand Electoral Roll - Onslow Main Roll for 1957, found in June 2018:
Leo, Muriel Thelma, 19 Stephen Street, married
Leo, Thomas William, 19 Stephen Street, civil servant

New Zealand Electoral Roll - Tamaki Composite Roll for 1963, found in June 2018:
Leo, Muriel Thelma, 53 Reihana St., E1., Married
Leo, Thomas William, 53 Reihana St., E1., Civil Servant

New Zealand Electoral Roll - Tamaki Main Roll for 1978, found in June 2018:
Leo, Muriel Thelma, 2/255 St Johns Road, Meadowbank, Widow
Leo, Graeme, 2/255 St Johns Road, Meadowbank, Technician [Son]

New Zealand Electoral Roll - Tamaki Composite Roll for 1981, found in June 2018:
Leo, Muriel Thelma, 2/255 St Johns Road, Widow
Leo, Graeme, 2/255 St Johns Road, Technician [Son]

Year and country of marriage from search on New Zealand BDM website in June 2023:
1946/1896. Bride: Muriel Thelma Oliver. Groom: Thomas William Leo

Full date of marriage of 21 January 1946 from further searching in June 2023 on BDM Search by incrementally changing the date range for the marriage.