Immediately after you enter the House of Deep Sorrow, you'll see her (in her human form) drained of her soul by three Exorcists or Shadows of Death. They will not attack you until you attack them, so she will shout on you to leave while you still can (which you can do at this point). If you kill the Reapers, Lady Victoria will become interactable. Upon speaking to her, she will say that the Reapers stripped her humanity from her, and will transform into a Succubus. She will have Electrified and Fast affixes.
Upon death, she will always leave The Horrible Secret book, revealing that her mother survived a demon attack, implying that the attack in question led to Victoria being half-human and half-demon (and thus more demonic than most humans in Sanctuary).