"The Ministry of Education indicates there is no targeted funding available for salaries such as hers, which is disappointing in light of the independent reports showing how far New Zealand lags behind the rest of the world when it comes to the care and protection of our tamariki," Mrs King said.
"There are so many people passionate about the welfare of our girls, and it's only fair and right that they get paid a fair wage for that."
Mrs King said the school's social worker was a very valuable member of staff, describing her as "incredible".
"[She] is always available to support our girls. She goes over and above the call of duty, is highly qualified academically and culturally equipped to deal with the unique nature of her role in Whanganui."
Mrs King said a key role of her job was to support the emotional well-being of students, as opposed to just meeting their academic needs.
"However, to do so schools need to be adequately resourced, something that is not currently happening and there is no indication that anything will change soon."
Mrs King noted a June 2017 report that showed New Zealand has the highest youth suicide rate in the developed world - ranked first out of 41 countries.
The rate of 15.6 suicides per 100,000 people is twice as high as the United States' rate and almost five times that of Britain.
"We work hard to support the emotional well-being of all our girls and we need to ensure we are adequately resourced to continue with the level of care and protection that should be a right for every Kiwi child," Mrs King said.
Chair of the Whanganui Community Foundation, Alaina Teki-Clark, said the foundation had provided $10,874 per year to Whanganui Girls' College, between 2011 and 2016, under its Social Initiatives in Schools programme.
"In 2016, the foundation reviewed its granting strategy. As part of that review, the foundation ended the Social Initiatives in Schools programme. In 2017, Whanganui Girls' College applied for a community support grant to support the school social worker. This application was declined."
Ms Teki-Clark said in general the foundation doesn't provide funding for operational costs to organisations receiving a high level of government funding, such as schools. But she said it recognised the need for students to receive pastoral care.
"Therefore, the foundation has written to the ministers of education and social development asking that they consider increasing both the operational funding for schools, which is available for student support, and the social workers in schools programme, so that schools are able to provide sustained and consistent learning support, mentoring, counselling and social work for the well-being of their students," she said.