After completing the University of Pennsylvania in 1895, she was formally awarded a Bachelor of Science degree.

Pennington was appointed head of the Food Research Laboratory by Harvey Wiley, the chief chemist of the USDA's Bureau of Chemistry. Here, she led pioneering research into food spoilage and preservation methods.

Pennington's research focused extensively on the refrigeration and storage of poultry. She identified the crucial factors affecting poultry spoilage and developed methods for chilling and freezing to maintain quality and safety.

The Pure Food and Drug Act was established. Pennington's work was vital in providing the scientific basis for enforcing the new regulations on food safety.

Pennington was appointed to supervise all the federal food control laboratories as well as the Food Research Laboratory. She was instrumental in creating and enforcing food safety standards across the country.

During World War I, Pennington's expertise was crucial in developing standards for refrigerated transport of food to troops overseas. This ensured the preservation of perishable goods and contributed significantly to the war effort.

After years of dedicated public service, Pennington resigned from her government position to pursue a career as a private consultant. She felt she could have a greater impact on the industry by working directly with companies and organizations.