She was elected to the Victorian Legislative Assembly as a Liberal Party member for South-West Coast, at a by-election in 2015.

Prior to her election, Britnell was the vice-president of United Dairyfarmers of Victoria (UDV), chairwoman of WestVic Dairy and was a Nuffield Farming Scholar in 2011.

[3] Britnell also served on a number of boards including the Geoffrey Gardner Foundation, Glenelg Hopkins Catchment Management Authority, Australian Dairy Farmers Federation, was Policy Councillor with the Victorian Farmers Federation, was a member of the Great South Coast Group's Economic Pillar and a committee member of the Warrnambool City Council's Food and Agriculture into China project.

[5] Britnell was pre-selected by the Liberal Party to contest the by-election to replace the retiring member for South-West Coast, former Premier Denis Napthine.

A total of nine candidates nominated, including incumbent independent member of the Legislative Council for Western Victoria Region, James Purcell, and former mayors of the City of Warrnambool, Kylie Gaston (Australian Labor Party) and Michael Neoh (independent), and former mayor of the Moyne Shire, Jim Doukas (Australian Country Party).