You use your new skills to convince her to put down her cross.

You look at the cross, then stare into her eyes, smiling sweetly.
"Come Harriet." You say, voice dripping with power. "Put that silly little thing away. Haven't you always wanted to break the bonds of religion? Haven't you always wanted to be a little bit naughty?" Her eyes become slightly unfocused and her cross holding hand lowers slightly.
"I-I-I-" She says, nervously. Your spell is working.
"C'mon Harriet." You say, taking a step forward. "You've never wanted to skip church on Sunday or have sex before marriage?" You pull your cock free. "You know you want to fuck me, I saw it the day we met. Well you can. I can put this penis to use a million different ways, if only you'll let me."
She stares at your cock awestruck, and finally the hypnotism washes over her. She smiles at you and drops the cross, the chain making a ringing sound on the hard floor.
"Yes Linus." She says. "I want- I want you so bad. I want you to fill me with your hard cock. Please Linus, can we?" She approaches, slender fingers out stretched, but you put up a hand.
"Well I don't know." You say teasingly. "I'm not sure if you really want it. I think you should have to prove it."
She looks distraught; "How?!" She sobs.
"Well." You say. "How about you show us whats underneath."
She looks down at her clothes, then smiles at you. She pulls off her jacket, then her shirt to reveal a practical black bra holding her small but firm breasts. She reaches back to unclasp the bra, then tosses it into a corner. She hardly needs it as her tits are very perky and keep their shape just fine. Her nipples are small and dark in colour. Then she reaches down to her skirt, pulling it down her legs and then stepping out of it. She begins to remove her black tights, but you step forwards and reach for it instead. She smiles, and watches you raptly. You pull her tights down so that they rest just below her small buttocks. Then you grab her boring black panties and rip them free, to which Harriet giggles girlishly. Her pussy is exquisite but surprisingly hairy. Clearly the woman was so repressed she never even shaved down there. You cup her cunt and she lets out a little gasp and locks eyes with you. You grin as you slip a finger inside, massaging her clit gently. She bites a lip, and holds on to your muscular chest, little exhalations signalling her arousal.
"There's one more thing you have to do before you can have my cock." You say.
She looks at you with eyes drowning in lust; "Anything." She exhales.
You pull in close, her nipples grazing your chest, and whisper: "Let me desecrate your body as you renounce your pathetic faith." You pull back expecting her to accept immediately, but the look on her face is one of doubt. You stroke her pussy harder: "It's the only way." You say firmly. She whines and moans, but you hold firm . Finally she gives in.
"F- Fuck god." She says. You smile, and nod for her to continue. "Fuck... Jesus, and church, and marriage, and all the saints." You laugh and she smiles, her voice growing louder and more confident. "Fuck... not fucking! Fuck crosses and congregations! Fuck priests!" She is yelling now. "Fuck nuns and vows! Fuck all that is holy and sacred!" You lean in close, inhaling her intoxicating scent. You move one hand around her waist (one still playing with her clit vigorously) and slide your cock between her legs, where it rests comfortably, its tip brushing her ass lightly. "Fuck sins and angels! Fuck sacraments and baptisms! Fuck God! Fuck me, make me your vampire whore!" You bite down, her blood flooding your mouth. She comes hard, screaming all the while. You gulp deeply, her orgasm's subsiding as her blood is exhausted. You hold her in your arms and watch her change. Her tits grow and press into you, her buttocks becoming much more firm and full in your hands. Her muscles tighten and grow, her stomach and arms becoming defined and beautiful. Finally, her fangs grow in her gaping mouth, and her eyes pop open glowing crimson. You kiss her and she grips you.
"So." She says as your lips part. "Now I'm your little whore, are you going to do what you promised?" You laugh and respond by shifting your penis to her labia. You tease her with the tip briefly, producing an animalistic whine from Harriet, then you push it in hard. She gasps as you lift her up with your cock so that she now looks down at you. Then, gripping her buttocks, you begin to pound her weeping cunt hard. She squirms in ecstasy, hands writhing over your shoulders, face turned towards the sky. You push your face into her breasts and breathe her scent deeply. You begin to approach climax, smashing her vagina harder and harder. Any mortal woman would have had ruptured flesh in seconds, but Harriet's vampire pussy merely begs for more. You come at the same time and she grabs your head to stare deep into your eyes as she wraps her legs around your waist. She shudders against you with each wave of orgasm but determinedly keeps her embrace, her labia pushed all the way down to the bottom of your shaft. Eventually, the orgasm ends, and she sighs with you, laying her head on your chest. You embrace for a moment, then she hops down to look at her sex. She parts her vulva lips, letting some of your seed drip into her tights. She smiles at you, then closes in for one last kiss.