You're inflamed with lust now, enveloped in a situation you'd never dreamed possible (on several levels). You continue to grind against her, kissing her, groping her member, her breasts. With each stroke, you feel her muscles tense, with every other, you feel her body pop, still changing. She pushes you off for a moment, pressing a thick finger across your lips.
"Lover," she says in her deep voice, husky, tinged with a bestial tone, "you have a choice, for this night comes with a price. If you wish, you may fuck me. If you fuck me, you will forevermore turn into a werewolf when you have sex at night, and be a beautiful woman by day. You'll have to make a new life for yourself, but a wondrous life it will be. Let me have my way with you tonight, and you'll change into a female werewolf when you have sex at night, but you'll be a man by day. You can keep the life you have, but you'll have a secret to keep from most everyone you know. Which do you choose, and be quick about it."
You ponder her choice.