Before being raised Amyrlin Seat she had been the Captain-General of the Green Ajah.
She was the Amyrlin Seat during the Third War of Garen's Wall. It is widely believed by historians that she completely mishandled the situation, and caused the war. It is also believed she died in the White Tower of natural causes.
Shein had attempted to rule the Tower with an iron hand, a plan that initially worked, but the Hall took control of her by punishing her with Mortifications of both Flesh and Spirit as reply to everything she said and did, heavily mishandling the situation. The Hall and the Ajah Heads had catfights over authority, and each faction of the Hall also had its own motives and causes, pulling the Tower in different directions. Eventually the sisters themselves rose up and pulled Shein and the Hall down in one of the six mutinies in Tower history. Shein was smothered to death fifty years later while in exile, after a plot to restore her to the Amyrlin Seat was discovered, and the entire story hidden away in the Thirteenth Depository.