While Borginnes was not involved in the Battle of Monterrey, she did see action during the Battle of Buena Vista. During the conflict she prepared food and coffee, reloaded weapons, and carried wounded off the field of battle. Her attention to the injured even earned her the nickname "Doctor Mary". Legend claims she received a saber wound to her cheek while working a cannon position before slaying the Mexican soldier who cut her. Another incident involves a retreating private. The soldier ran into Borginnes' restaurant yelling that Taylor had been defeated. She responded by punching the private in the face and telling him "You damned son of a bitch, there ain't Mexicans enough in Mexico to whip old Taylor. You just spread that report and I'll beat you to death."