Also known as Formal Royal's Wife or Singing Lady.
A female vendor who appears to have endured horrific torture; her face and hands (and likely more under her dress) have been horribly mutilated. In addition her eyes are closed and she bleeds tears indicating she is probably blind. Perhaps her eyes were plucked out as a part of the torture. She can be found in a cell in the first area of the Tower of Latria, listen for the singing to locate her.
This former wife of royalty is also a prisoner in Latria's dungeon but has much better accommodations than the other prisoners. She has a variety of goods left over from when she was royalty and offers to sell them to the player to gain souls and maintain her sanity. It is from her that the player learns much of what has transpired in Latria since the coming of the Deep Fog. To pass the time in her cell she sings a haunting melody.
The female vendor in the dungeon of Latria mentions that she was once the "wife of royalty." The phrasing indicates that her husband was of noble blood and she is only royalty by marriage. She also never outright says whether her husband was killed or if other circumstances ended their marriage. It is possible her husband is of no consequence but there are many theories linking her to various other characters in Latria.
Since the Royal Mistress has inside knowledge about the Fool's Idol (facts not known to most of the other prisoners), that it is an imposter and has the ability to resurrect, it is likely that her husband was one of fairly high station. If he is alive, possibly he is one of the prisoners who know magic such as the groups of four which hold the massive chains in place or the Liar who resurrects the Fool's Idol.
The Mistress may also sell the player the Ring of Avarice, a symbol of wealth and debauchery. This further hints at her former royalty.