Well, last night we tried the whole idea of sitting outside of Olivia's room and just putting her back in bed every time she got out. After an hour of this, I got so frustrated that I started yelling, and Joe had to step in. He managed to get her to stay in bed, and a half-hour later she fell asleep by herself in her bed. And she slept through the night, which she's only done twice since Christmas (don't ask why, we don't know). And away we go.
We decided on this strategy of explaining to her that she'd need to be a big girl and sleep by herself and stay in bed, and then we'd keep our vigil right outside her room until she actually did fall asleep. Every time she gets up, we're supposed to put her back in bed without talking to her. She does the usual things..."Mommy, I need a kiss. I need socks. I need a blanket." We don't respond unless she gets out of bed.
Ultimately, I think this will eventually work. But we are going to have to be very, very patient for weeks until we have great success.
I'm still open to any suggestions. We've tried shutting her in her room, but she will get up and turn on the light and play, peeking out the door to get our attention so we'll come in the room and put her back in bed. It's a game for her. I think the key is to ignore her as much as possible and she'll (eventually) get the idea that bedtime is not playtime and we aren't playing her games any more.