She reveals she worked in an old bookstore which had been built in the 1950s and equipped with a fallout shelter which was converted into the basement.
It differs from a fallout shelter, in that its main purpose is to protect from shock waves and overpressure, instead of from radioactive precipitation, as a fallout shelter does.
The new school was substantially larger than the old 4-classroom building, with a cafeteria which doubled as a fallout shelter, a gymnasium and locker rooms, and many more classrooms.