Born in Gosford to parents John and Joy,[1] Trewhella planned a career as a high school mathematics teacher in Newcastle,[2] but after the death of her brother enrolled at his alma mater, the University of New South Wales,[3] where she received a Bachelor of Science degree with a double major in applied mathematics and physics and first class honours in physics in 1974.

[1] She also received her MSc in physics from UNSW before moving to the University of Sydney to complete her PhD in inorganic chemistry supervised by Peter Wright in 1980.

[6] In 2015, Trewhella took up the Tage Erlander Visiting Professorship in Sweden, based mainly at Linköping University,[7] where she networked with Swedish researchers to develop projects that would take advantage of new infrastructure for X-ray and neutron scattering studies to characterize materials, including biological materials where the object was to understand biological function and provide a foundation for advances in medicine and biotechnology.

Trewhella's research focuses on the use of chemistry, physics and computational methods to study bio-molecular structures as a basis for understanding their functions.

[2] She holds a joint appointment at the Bragg Institute within the Australian Nuclear Science and Technology Organisation (ANSTO) and is an adjunct professor of chemistry at the University of Utah.