CHARLESTON, S.C. — The gentle pace of life on the campus of Ashley Hall, South Carolina’s only all-girls preparatory school, appeared to be back on Friday. Parents lined up in the shade of the live oaks to pick up their children. A luncheon for alumnae of the school, which was founded in 1909, went on as planned.

Still, police officers patrolled the iron fence that surrounds the school and teachers remained on edge, trying to grasp how a woman with a public history of mental illness had managed to buy a gun a week earlier and amazed that the gun, when pointed at administrators who confronted her in front of the school on Monday, did not fire.

Alice Boland, 28, who was charged in 2005 with threatening to assassinate President George W. Bush and members of Congress as she waited in line at U.S. Customs, is again charged with plotting a violent attack. On Monday, after pacing in front of the school gates during car pool and visibly swinging a gun, she tried to shoot two faculty members: the director of the high school, Mary Schweers, and an English teacher, Chris Hughes.

The police charged Ms. Boland with attempted murder and unlawful carrying of a firearm. The only thing that stopped her, they said, was that she did not realize the gun was locked.