Silvestri obtained her medical degree from the University of Rome La Sapienza in 1947. She married Romanian diplomat Nicholas Timiras and then moved with him to Canada where she studied experimental medicine and surgery at the Université de Montréal, gaining her doctorate in 1952. During her postdoctoral work at the University of Montreal her supervisor was the endocrinologist Hans Selye. One of Timiras's colleagues was Roger Guillemin.

Timiras performed her doctoral research at the University of Montreal in the lab of Hans Selye, who had developed the first theories about the body's hormonal responses to stress. At his suggestion, Timiras applied for and won a research fellowship that allowed her to work in his lab. There, she studied how stress influences the immune system through the effects of adrenocortical hormones.

Before she finished her degree, the University of Montreal hired her as an assistant professor. In 1954, she moved to Salt Lake City to pursue that line of inquiry in the pharmacology department at the University of Utah. In 1955, she joined the University of California, Berkeley physiology department as an assistant physiologist and was appointed to the faculty in 1958. She became a full professor in 1967.

At UC Berkeley, Timiras studied the effects of caloric restriction on various hypothalamic nuclei, specifically the effects on cell density, estrogen receptor alpha (ERα) immunoreactivity and insulin-like growth factor-1 (IGF-1) receptor immunoreactivity.

She died in September 2008.