Given the task definition and input, reply with output. In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.

Passage: One evening near the small Serbian village of Stetl, early in the nineteenth century, schoolmaster Albert Müller witnesses his wife Anna taking a little girl, Jenny Schilt, into the castle of Count Mitterhaus, a reclusive nobleman rumored to be a vampire responsible for the disappearances of other children. The rumours prove true, as Anna, who has become Mitterhaus' willing acolyte and mistress, gives Jenny to him to be drained of her blood. Men from the village, directed by Müller and including Jenny's father Mr. Schilt and the Bürgermeister, invade the castle and attack the Count. After the vampire kills several of them, Müller succeeds in driving a wooden stake through his heart. With his dying breath, Mitterhaus curses the villagers, vowing that their children will die to give him back his life. The angry villagers force Anna to run a gauntlet, but when her husband intervenes, she runs back into the castle where the briefly revived Count tells her to find his cousin Emil at "the Circus of Night". After laying his body in the crypt, she escapes through an underground tunnel as the villagers blow the castle with gunpowder and set fire to it.
Who becomes Count Mitterhaus' mistress?