Question: When did the school where Mandy Edwards studied become co-educational ?

Context paragraphs:
Richard Edwards (educator): Richard Edwards (December 23, 1822 – March 7, 1908) was a Welsh American educator from Cardiganshire.  Emigrating to the United States with his family when he was a child, Edwards studied at the State Normal School in Bridgewater, Massachusetts and Rensselaer Polytechnic Institute in Troy, New York.  He then led a number of schools: the Boys' High School in Salem, Massachusetts (1853–1854); the State Normal School in Salem (1854–1857); the Normal School in St. Louis, Missouri (1857–1861); Illinois State Normal University (1862–1876); and Blackburn University (1891–1893).  From 1887 to 1891, he served as the Illinois Superintendent of Public Instruction.

Ellerslie Girls' High School: Ellerslie Girls' High School was a girls' public high school at 355 Main Road, Sea Point, Cape Town, South Africa.  The school was established in 1898.  In 1989 the school merged with Sea Point High School, formerly Sea Point Boys' High School, which had become co-educational.

Chatham Grammar School for Boys: Holcombe Grammar School (formally Chatham Grammar School for Boys) is a grammar school with academy status in Chatham, Kent, England.  It is a selective school.  From the 2017-18 academic year, the school planned to become co-educational and remain selective in the lower school.  This was blocked - and later approved - by the Department for Education with co-educational admission desired for the 2018/19 school year.  The school has changed name in advance of becoming co-educational and plans to change all references from "Chatham Grammar School for Boys" to "Holcombe Grammar School" over academic year 2016/17.

Mandy Edwards: Mandy Edwards (born 28 July 1982) is an Australian netball player.  In 2008, Edwards was signed to play in the ANZ Championship for the Adelaide Thunderbirds.  Edwards was educated at Westminster School in Adelaide.

Van Mildert College, Durham: Van Mildert College (known colloquially as Mildert) is a college of Durham University in England.  Founded in 1965, it takes its name from William Van Mildert, Prince-Bishop of Durham from 1826 to 1836 and a leading figure in the University's 1832 foundation.  Originally an all-male college, it became the first Durham college to become co-educational in 1972 with the admission of female undergraduates.

Alpha Delta Phi: Alpha Delta Phi (ΑΔΦ, also "Alpha Delt," "A.D." or "ADPhi") is a North American Greek-letter secret and social college fraternity.  Alpha Delta Phi was originally founded as a literary society by Samuel Eells in 1832 at Hamilton College in Clinton, New York.  Its more than 50,000 alumni include former presidents and senators of the United States, and chief justices of the Supreme Court.  In 1992, five chapters withdrew from the male-only organization to become co-educational, and formed the Alpha Delta Phi Society, a separate and independent organization.

Wesley College, University of Sydney: Wesley College is a Protestant co-residential college of 250 students within the University of Sydney.  The College occupies a site on the main campus of the University of Sydney and was built on a sub-grant of Crown Land.  Wesley is one of six on-campus colleges at the University of Sydney which provide accommodation.  In 1923 the college averaged 45 students.  Originally the College accommodated only men but when women were admitted in 1969 Wesley became the first of the colleges within the University of Sydney to become co-educational.  Its current head is Lisa Sutherland, who has held the position since 2010.

List of alumni of Jesus College, Oxford: Jesus College is one of the constituent colleges of the University of Oxford in England.  Its alumni include politicians, lawyers, bishops, poets, and academics.  Some went on to become Fellows of the college; 14 students later became Principal of the college.  It was founded in 1571 by Queen Elizabeth I, at the request of a Welsh clergyman, Hugh Price, who was Treasurer of St David's Cathedral in Pembrokeshire.  The college still has strong links with Wales, and about 15% of students are Welsh.  There are 340 undergraduates and 190 students carrying out postgraduate studies.  Women have been admitted since 1974, when the college was one of the first five men's colleges to become co-educational.  Old members of Jesus College are sometimes known as "Jesubites".

Westminster School, Adelaide: Westminster School is an independent, Uniting Church, Early Learning to Year 12, coeducational, day and boarding school located at Marion, South Australia, 12 km south of Adelaide.  Founded as a Methodist day and boarding school for boys, the school was opened by the Prime Minister Robert Menzies in 1961 and is named after Westminster School in London.  The school became co-educational in 1978, and has a current enrolment of around 1150 students.

List of clergy educated at Jesus College, Oxford: Jesus College is one of the constituent colleges of the University of Oxford in England.  The college was founded in 1571 by Queen Elizabeth I at the request of Hugh Price, a Welsh clergyman, who was Treasurer of St David's Cathedral in Pembrokeshire.  The college still has strong links with Wales, and about 15% of students are Welsh.  There are 340 undergraduates and 190 students carrying out postgraduate studies.  Women have been admitted since 1974, when the college was one of the first five men's colleges to become co-educational.  Old members of Jesus College are sometimes known as "Jesubites".

Supporting paragraphs: Mandy Edwards Westminster School, Adelaide
Answer: 1978