Try talking to her

"Yes," you say. "I'm Brenden. Let me go!"

She releases you out of shock. As for you, you'd been pulling against her grip much harder than you realized, and the moment she lets go you lose your balance and fall right on your butt. She helps you to your feet, and as you brush yourself off, you realize that while Emily may have been turned into a vampire by her costume, she's still Emily inside, and you're still Brenden. You can't see her attacking you or you running from her anymore.

"This is super weird," she says, looking you over. "But also kind of hot."

"Yes," you say. "I wonder if the same thing is happening to the other partygoers."

She looks around, but you seem to be alone in the foyer at the moment. "So what do we do?" she asks