Coming from a noble family, Wendy was kidnapped by the Guild as a child after the Hand of Shadow discovered that her family owned the "Shadowghost Cloak" since various generations, one of the ancient relics of the early years of the Thieves Guild, a cloak that make anyone who wear it invisible. The Greywing family refused to give up the magical cloak in exchange of their daughter, replying that a child life was not worth their honor and treasure.
The Shadow Hand should have killed the child but decided instead to raise her with Aaron, who was just few years older than her, in the only way the guilds know.
As one of the most feared thieves in the guild in her adulthood, she decided to take revenge on her family by stealing the Shadow Cloak, just to discover that the it was not magical at all but simply an ornamental object.
Today, Wendy wears the cloak as a trophy as she robs her favorite victims from the nobles of the kingdom of New Torm.