Unless stated otherwise, all information herein is taken from Towers of Midnight, Chapter 24.
Sigril is Yoeli's sister. She leads the Lastriders. After the battle of Maradon, they watched the city and alerted the rest of Saldaea.
Sigril's name is based on the real-life name of Enya Tawarwaith, an Aes Sedai of the White Ajah at TarValon.Net.