I made up a lore reason if anyone is interested: she was the central part of the plot conspired by Svartalfars who were fed up with the war. It consisted in the assassination of Faeryl Viconia. Volanna was the voluntary assassin and succeeded. Afterwards, the Svartalfars were kicked out of the Ljosalfar lands with a 'thanks but you're bastards'. Instead of staying with their new leader, Volanna chose to go somewhere else and eventually become a Grigori adventurer.