She had remained loyal to the White Tower during the split.
Several years ago, Josaine found an angreal and kept it to herself. Alviarin ordered Elaida to personally search Josaine's room, as well as Adelorna's, as Adelorna had removed an angreal from the storeroom without permission.
When Elaida found the angreal, she was to give stiff punishments to both sisters. At the same time, Alviarin ordered Elaida to reward Doraise, Kiyoshi and Farellien (a Brown, a Gray and a Yellow), which will make it seem as if the latter three had exposed the former two. Elaida wanted to know why Alviarin was ordering this, as it will create dissension between the Ajahs.
Josaine and Adelorna were birched. The same day Seaine thought to herself that never in living memory have two sisters been birched for holding back angreal. This had created strife and division between the Ajahs.
During the Seanchan attack on the White Tower, Josaine stood with Marthera and Adelorna to fight the invaders. The group was defeated within minutes, with Josaine dead from an explosion of Earth that took out part of the Tower wall.