You have a cunning plan...

You have an idea, but you are not sure it will work. Still, there's only one way to find out...
You sink to your knees before her, fake tears spilling from the corners of your eyes.
"Please..." You say in as grief stricken voice as you can muster. "I don't want to be like this anymore... You have to help me Harriet, you're the only one who can." You break into a sob.
The woman looks bewildered: "What? W- why me?"
You cry some more: "Your faith. Only your faith is strong enough to turn me back to normal."
She looks taken aback, but you think you see something there, a hint of arrogance perhaps.
"Please! Excise this demon before I hurt anyone else!" You bury your head in your hands.
She swallows hard, but seems to take your words on board: "O-okay! I'll try my best!" She holds her cross out with greater conviction. Now is the moment of truth. Somewhere in your new vampiric brain you seem to know that you can disguise yourself, but you are not totally sure. Nevertheless, with a pang of sadness, you compel your skin to regain its mortal colour and your fangs to hide in your gums, at least for now. All the while Harriet shouts: "The power of Christ compels you!" And other such tosh. You twist and writhe in "Agony" but the words have no effect. Eventually, cued by your loud scream, she stops, breathing heavily. Slowly, you rise.
"Y-you... your cured!" She says, stepping closer. "How do you feel Linus?" She caresses your face tenderly.
"I feel..." You take her hand and hold it against your face, feigning discomfort. "...Hungry!" You growl, your eyes turning cruel as your disguise melts away in an instant. She screams and tries to pull away, but it's too late. You slide your fangs into her wrist, sucking her blood, taking as much as you can. She screeches and swings her cross at you, but you let go of her and dodge easily. She turns and begins to run, but her legs give out under her due to the blood loss. She regains her footing and shambles along the corridor clutching her wrist as your follow at a leisurely pace.
"Give in Harriet! Can't you feel it in your wrist? That's true power, not your phony religion." You call after her.
"Never!" She snarls back. You can't help but admire her conviction.
You laugh sweetly; "Come now, your blood is going everywhere! You don't want to be wasteful, do you? Let me finish you off and we can be together, as equals." Her movements are slowing now, and eventually she comes to a complete standstill. She turns, tears in her eyes.
"Is it... is it good?" She asks quietly.
You smile kindly. "Better than you could ever imagine. Your faith is holding it back I think, but if you just let my bite work, you can become just like me. All you have to do is give in." She sobs and stares at her hand. You stand like this for what seems like an eternity, the only sound is the faint dripping of her blood. Then, she lets her cross fall. The change happens rapidly as her arm stops bleeding and you see her talons grow. She looks at her vampire hand with bemusement, then watches the other go pale and grow talons too. She lets her jacket drop then pulls her top off, buttons ricocheting on the floor. You watch as the pale vampiric skin spreads over her chest, expanding her perky breasts. She opens her mouth, and you see her canines lengthen. She licks her new fangs with her lengthening tongue, and smiles as her eyes become deep crimson.
"Mmmmm." She moans, massaging one tit. "This is better than I could've imagined." She reaches down and grabs her waistline, pulling her skirt and underwear free in one go. Her hairy cunt is dripping, and she jams two fingers into it, mashing her clit violently. You begin to pleasure your own sex as she writhes and crouches, the ecstasy too much to bear standing. She moans and squeaks often shouting "Yes! Yes!" at the top of her lungs. Then she comes, her sweet pussy vibrating and quivering as she does. This pushes you over the edge and you approach, spraying your load onto her willing face and tits.
"Mmm yes. Thank you for your gift." She licks some of the cum dangling from her lips and gently kisses the tip of your penis. You pull her up so that your faces are close together.
"See? Told you it was good." She giggles and grips your ass, pushing her breasts into your chest.