Mili Skane is the daughter of a saddler from a village near Whitebridge.
She is 5'4 tall, sharp-featured but pretty. Her face is delicate but vulpine. She has glossy brown hair that she brushes to glossines and hangs below her shoulders, and big brown eyes.  There was no warmth in her face; it seemed to lack feeling. She spoke with almost the accents of an Andoran noble.
As a young girl, she went to the White Tower to become an Aes Sedai. When she discovered she couldn't channel, she became a Darkfriend. Within the year she had killed her first man - her first nonpersonal murder, anyway. Over the next seven years, she would commit nineteen assassinations; her kills for personal reasons were more than double that.
She was considered one of the best assassins, able to find anyone or anything. She led a circle which included several nobles, and most were older than she.
Mili murdered Willim Avarhin, his daughter, Shiaine, and their lone servant, and has taken on Shiaine's identity. She murdered them for the sole reason of taking on Shiaine's identity, as it would be useful to pretend to be the last daughter of a minor noble family going back to the founding of Andor. Murdering Willim also got her access to his money. Mili felt that only a few Darkfriends knew her secret, and that the reclusive lives of the Avarhins would make it unlikely she would be found out.
She attempts to kill Rand and Mat in a stable but Mat foils the attempt and locks her up before they leave. She keeps this a secret, as she preferred people to believe she had failed to find them, rather than that she had failed to kill them and had allowed them to escape.
In Ebou Dar she was under the command of Old Cully and Jaichim Carridin to find the cache of ter'angreal, sa'angreal, and angreal that was within the city. When Carridin spots Mat he instead places her in charge of finding and killing him.
She hated Carridin for mistreating her, and for finding out that she had been embezzling gold to support her gambling habit.
Lady Shiaine takes up residence in Caemlyn on orders of Moridin, who also told her to kill Carridin - a task she enjoyed immensely. Moridin also gave her Falion Bhoda, who was given to Shiaine to use and punish for her failure in retrieving the angreal and ter'angreal stash in Ebou Dar. Falion is mostly used as a servant, as well as being given to Daved Hanlon, though the two merely exchange information. Shiaine also gives orders to Hanlon, sending him to the Royal Palace to become a guard and get close to Elayne Trakand. She also gave him the order to free the captive sul'dam in the palace and to burn Caemlyn's food warehouses. Marillin Gemalphin was also sent to serve Mili.
Although Mili would have groveled for Darkfriends above her such as Old Cully, she had gained the protection of Moridin.
Mili's main mission was to create chaos in Andor, which she succeeded at by arranging arsons and creating conditions for crime.
Because of Shiaine's "easy" treatment of Failon, Murellin is asked by Moridin to come to Caemlyn and remind Shaiaine that Falion is her dog, in a manner unclear, but involving Murellin having use of Falion when Hanlon is not present. 
Eventually, Elayne, Vandene Namelle, Careane Fransi, and Sareitha Tomares find her, along with Falion and Marillin Gemalphin, at Shiaine's house on Full Moon Street. Recognizing them as Black Ajah and Darkfriends, Elayne and the other Aes Sedai attempt to capture them, but are thwarted by the return of Asne Zeramene, Chesmal Emry, Eldrith Jhondar, and Temaile Kinderode. Careane is revealed as Black Ajah, and the murderer of Ispan Shefar and Adeleas, Vandene's sister, and some members of the Kin. Vandene kills Careane, but Chesmal kills Vandene as well as Sareitha.
The Black Ajah sisters kidnap Elayne from the city but she is rescued by Birgitte, who had felt the incident through her Warder bond, and the Windfinders at the Palace. Asne is killed in the fight and the rest of the Black Ajah sisters and Lady Shiaine are taken to the Royal Palace dungeons.
She is rescued from her cell by Hanlon during Elayne's interrogation attempt of the Black sisters, which turns into a scuffle. She manages to escape from Caemlyn and is still at large.