Turn her down.

"It's tempting, but no thank you," you say gallantly. "I want to stay faithful to my girlfriend." You're not sure that you believe this excuse, but it sounds good and there's something about her aggressiveness that you find very off-putting.

"That's sweet," she says, still cheerful, "but if you change your mind, just whistle. You know how to whistle, don't you?"

You nod dumbly, not getting the reference and she walks out the door, closing it behind her.

A little bewildered, you lie down on your new bed and relax for a bit. You must have dozed off for a bit because the next thing you know there's a knock on your door and you're startled out of sleep.