Diaconescu was born in Romania and received a Bachelor of Science degree from the University of Bucharest in 1998 conducting research on transition metal complexes and f-block metals. In 2003, Diaconescu received a PhD in chemistry from the Massachusetts Institute of Technology working with Christopher C. Cummins on uranium chemistry. Before joining the faculty at UCLA in 2005, she spent two years as a postdoctoral fellow at the California Institute of Technology with Robert Grubbs.