She masturbates

When Buffy woke up her fingers immediately went to her snatch. She plunged three fingers in, her thumb working her clit, her other hand moving to her breasts. She made herself come in just a few minutes. Buffy briefly wondered what had caused such behavior when she heard a voice whisper to her. "Good girl."

"What!? I thought... You were a dream."

"Sorry. And with that behavior you're off to a good start.

The creature that had Buffy wasn't exactly malicious. Centuries before a young women with some power but not the best lookign had wished herself more desirable to attract a man. After that she had lived "happily ever after" as they say, but before she'd died she'd wished other women the same happiness she felt, creating the being that had possessed Buffy.

It had examined her mind to find the best way to affect her, it had discovered he was a Slayer. It might be able to use her own supernatural power to add to it's own and speed the process. Or it might be able to add her power and actually split itself to affect another woman.