Jezrail is a dark, square-faced Tairen.
Jezrail does not show too much deference to Katerine, so she can't be too weak.
Jezrail almost married a young man before she came to the White Tower. She still keeps a miniature of him and speaks fondly of him, even though his grandchildren would be grandparents now. That would probably make her over one hundred years old, likely even older.
She prevents Katerine Alruddin from using the One Power to punish Egwene al'Vere when she makes a display in a novice class by splitting her in fourteen ways, a deed that impressed Jezrail. She grabs Katerine's wrist and admonishes her for going too far. Jezrail also seems to dislike anything related with forkroot.
Jezrail is one of the Red sisters, along with Pevara Tazanovni, Javindhra Doraille, Desala Nevanche, Melare, and Tarna Feir, sent to the Black Tower to put the proposition of Red sisters bonding Asha'man as Warders to Mazrim Taim. He has agreed to this.
Jezrail was probably turned to the shadow because Pevara affirmed the only herself among her group was able to escape the turning. This is later confirmed by "The Wheel of Time Companion".