Diem graduated with a Bachelor of Applied Science (Hons) from the RMIT University in 1996 and completed her PhD in 2001 at the University of Melbourne. She was awarded the NHMRC C.J. Martin/Peter Doherty Fellowship in 2002, worked at the College de France in Paris and later moved to the Molecular Biology Unit at the Baker Heart Research Institute. In 2005, Diem took up the role as a project co-ordinator for the Australasian Society of Cardiac and Thoracic Surgeons (ASCTS) Cardiac Surgery Program.

Diem joined the Department in 2007 as a Research Fellow for CCRE Therapeutics when the ASCTS project moved to Monash University. The Program records details of all adult cardiac surgical procedures performed in participating units and now includes 19 of 24 public hospitals and 6 private centres in Australia. The Program publishes annual reports describing the activities and outcomes of participating units in a comparative, de-identified format. The ASCTS group has published 10 papers in peer reviewed journals and an additional 2 manuscripts in collaboration with the MIG group.