The Lady is a Hullen entity that lives entirely within the Green Plasma in season 3 and 4 and escapes from the Green in the end of season 4.
The Story of The Lady
Black Root Officers told Khlyen that they were to escort him to The Lady shortly after he let D'avin Jaqobis escape the Red 17 facility on Arkyn. While Dutch is in Aneela's memories from The Remnant, Aneela says that the Green speaks to her, specifying that the Green is "she". Later Dutch sees both Aneela and Khlyen speak of The Lady, and how displeased she would be that Aneela created Dutch. In Season 4 The Lady is seen taking various forms in order tor torture Aneela, Dutch, Johnny and D'avin when they are in the Green. In the finale of Season 4 The Lady escapes from The Green disguised as Aneela, takes over the body of a female Westerlyn child and erases the memories of everyone in Old Town. She appears as a small girl first and then a teenage girl, but chooses to stay in the body of the teenage girl for the rest of the season. But because human bodies are so fragile and she cannot take over the bodies of the Hullen she wants to steal the body of Aneela and Kendry and D'avin's son as he is half human half Hullen. The reason for this is because The Lady's actual body can only survive in certain environments so she cannot live freely in the Quad with her own body as she will die. So her body was stored on the Armada the ship she stole from Aneela. She winds up failing at this mission as Dutch and Khlyen trap her in the very same mirror box Khlyen trapped Aneela in for centuries and D'avin,Jaq and Johnny kill her body making it so she is just a normal human teenage girl. Unfortunately the teenage girl who originally inhabited the body is dead.