[2] After three years of family medicine residency at the U.S. Army hospital in Fort Belvoir, Virginia, she served as a full-time officer for 13 months in the Sinai Peninsula.

She admired the order for their humility and making only minor changes over the years, noting that the "storm of Vatican II blew over their heads, and all they felt was a little breeze.

In 2003, she served at the Walter Reed National Military Medical Center in Washington, in 2005 at Fort Carson in Colorado, and in 2008 she was deployed to Afghanistan, where she cared for wounded citizens.

[16] On March 9, 2022, Byrne with the Thomas More Society filed a lawsuit against Muriel Bowser, LaQuandra Nesbitt, and the District of Columbia for denying her a religious exemption to its COVID-19 vaccination mandate for health care workers.

In August 2021, the district had begun requiring vaccination for health care workers, including exemptions for medical or religious reasons.

Byrne's application for exemption was denied and decided to file the lawsuit on the basis of the Religious Freedom Restoration Act, after the city suspended her medical license for remaining unvaccinated.

[20] On March 15, Byrne received a letter from Bowser, notifying her that she was granted a religious exemption to the COVID-19 vaccine, allowing her to resume her work as a surgeon and physician until 2023.