Twin sister of course

You approach Sabrina and remove the gag from her mouth. She coughs when you take it out, drool running down her chin.

"What's your twin sister's name?" you ask.

"Katherine," Sabrina squeaks out.

You grab Sabrina's phone and ask Sabrina for Katherine's number. You dial it in and bring the phone up to Sabrina's ear.

"Invite her over and do as I told you."

Katherine picks up and Sabrina speaks to her briefly, asking for some help on some relationship issues. Katherine agrees to come over and talk, and you hang up the call.

"I'll wait outside in my car, you can text me when Katherine has been given the pills and is asleep," you say, "I'm going to untie you now. When you hear the front door close, you may take off your blindfold."

Soon after you are waiting in your car, when you see another car pull up to Sabrina's apartment. A woman gets out, you can't see her clearly in the dark but about thirty minutes later you get a text from Sabrina.

Sabrina: I gave Katherine the pills in a drink right after she arrived so she's just dozed off.

You: Ok unlock your door and put your blindfold back on. Lie back in the same position on your bed as before.

You then head back up to Sabrina's apartment.