Rachel

Sometimes called Rachel and sometimes Paula, due to a name hiccup later on in the series, she was an assistant to Bianca St. Claire, who was fed upon and killed during Storm Front. The door to the library opened, and the straight-haired young woman who had greeted me earlier entered the room. She gave me a passing glance, then walked past me, kneeling at Bianca's side. Rachel, I presumed. Rachel murmured something too soft to hear, gently brushing Bianca's hair back from her face with one hand. Then she unbuttoned the sleeve of her blouse, rolled it up past her elbow, and pressed her wrist to Bianca's mouth.''
 * ''"Go," Bianca whimpered. Fury, hunger, and some emotion I couldn't even begin to fathom made her voice stretched out, thinner. "Go. And do not think that I will not remember this night. Do not think that I will not make you regret it."
 * ... Rachel wasn't coming out. 

Her death incites Bianca to seek revenge against Harry, who she feels is responsible for her death. This is the cause for most of the plot of Grave Peril, of which the aftermath is the plot for many of the other books as well. I returned the gesture, only more shallowly, just to throw the little zing of insult into it. "I remember. She was pretty. Polite. I didn't really get to meet her much." "No. She was dead within an hour of you setting foot in my house." "I thought she might have gone that way," I said. "That you might have killed her, you mean?" "Isn't my fault if you lost control and ate her, Bianca." She smiled, teeth blinding white. "Oh, but it was your fault, Mister Dresden. You'd come to my house. Provoked me to near madness. Forced me to go along with you under threat of my destruction." She leaned forward, giving me a glimpse down the flame-dress. She was naked beneath. "Now I get to return the favor. I'm not someone you can simply walk over, slap around, whenever you have a need. Not anymore." She paused and then said, "In a way, I'm grateful to you, Dresden. If I hadn't wanted so very badly to kill you, I would never have amassed the power and the contacts that I have. I never would have been elevated to the Court." She gestured to the crowd of vampires below, the courtyard, the darkness. "In a way, all of this is your doing."'' Harry also meets Rachel's ghost, in chapter 34 of Grave Peril: "Rachel," I whispered. "Rachel, is that you?" As I spoke her name, she turned to me, her eyes slowly focusing on me, as though beholding me through a misty veil. Her expression turned, no pun intended, grave. She nodded to me in recognition. "Hell's bells," I whispered. "No wonder Bianca got stuck on a vengeance kick. She literally was haunted by your death." The spirit's face twisted in distress. She said something, but I could hear it only as a distant, muffled sound accompanying the movement of her lips. "I can't understand you," I said. "Rachel, I can't hear you." She almost wept, it seemed. She pressed her hand to her ghostly breast, and grimaced at me. "You're hurt?" I guessed. "You hurt?" She shook her head. Then touched her temple and drew her fingers slowly down over her eyes, closing them. "Ah," I said. "You're tired." She nodded. She made a supplicating motion, holding out her hands as though asking for help. "I don't know what I can do for you. I don't know if I can help you rest or not." She shook her head again. Then she nodded, toward the door, and made a bottle-shaped curving gesture of her hands. "Bianca?" I asked. When she nodded, I went on. "You think Bianca can lay you to rest." She shook her head. "She's keeping you here?" Rachel nodded, her ghostly, pretty face agonized. "Makes sense," I muttered. "Bianca fixates on you as you die tragically. Binds your ghost here. The ghost appears to her and drives her into a vengeance, and she blames it all on me." Rachel's ghost nodded. "I didn't kill you," I said. "You know that." She nodded again. "But I'm sorry. I'm sorry that me being in the wrong place at the wrong time set you up to die." She gave me a gentle smile.''
 * ''She fell quiet for a moment, thoughtful. Then she asked me, as she formally inclined her head, for the benefit of the crowd below, "Do you remember Paula, Mister Dresden?"
 * ''The ghost took shape before me, very slowly, very translucently. It resolved itself into the form of a young woman, attractive, dressed like an efficient secretary. Her hair was pulled up into a bun, but for a few appealing tendrils that fell down to frame her cheeks. Her ghostly wrist was crusted with congealed blood, spread around a pair of fang-punctures. Abruptly, I recognized her, the girl Bianca had fed upon until she died.