The subject of this article or section originates from non-canonical sources. To find out about what is considered "canon" see LOTR:Canon.
Marwen ruled the lands of Núrn shortly before and in the early years of Sauron's return to Mordor. At some point, she became the mother of Lithariel. At some point prior to Sauron's removal from Dol Guldur, however, she was possessed by the wizard Saruman in his quest to find the One Ring, and was as a result aged prematurely, falling into a state of atrophy.
Eventually, Lithariel brought the ranger Talion to Marwen's court at what she believed to be the queen's command. Through Marwen, Saruman sent the ranger on a series of missions in hopes of bringing the wraith of Celebrimbor under his control. This was unsuccessful, however, as Talion and Lithariel were able to break Saruman's hold over Marwen, restoring her mind and appearance to their natural state.
Marwen then assisted Talion in preparing for his assault on The Tower of Sauron, which proved successful. However, in his absence, the Black Hand invaded Núrn and ravaged much of the land, including Marwen's stronghold. She is presumed to have been killed along with Lithariel, but her fate is ultimately unknown.