Dr. Gallagher attended Fordham University in New York as an undergraduate. She earned a degree in theology (MDiv) at Weston Jesuit School of Theology in Cambridge, MA (now The Boston College School of Theology and Ministry). After receiving her MD degree from Georgetown University School of Medicine in Washington D.C., she completed her residency in Obstetrics and Gynecology at the National Naval Medical Center in Bethesda, MD (now The Walter Reed National Military Medical Center) and a fellowship in Maternal-Fetal Medicine at The Johns Hopkins Hospital in Baltimore. After her fellowship, she served as head of the Maternal-Fetal Medicine division at Naval Hospital, San Diego, and then as head of Maternal-Fetal Medicine at National Naval Medical Center, in Bethesda.
From there she joined the clinical faculty at Harvard Medical School and practiced at Massachusetts General Hospital in Boston. During this time, she also served as the director of obstetrics at the Cambridge Health Alliance in Cambridge, MA. She returned to the Washington area to join Greater Washington Maternal-Fetal Medicine and Genetics, a private practice based in Maryland in 2003. She joined the faculty at the George Washington School of Medicine and Health Sciences in 2015 as a clinical associate professor in the Maternal-Fetal Medicine Division of the OB/Gyn department. She is actively involved in teaching George Washington University Obstetrics and Gynecology residents at GW University Hospital and at Holy Cross Hospital and has an active interest in medical ethics.