How to talk to a deathly shy girl?

I met a really shy girl a few weeks ago at a house party. We caught eachothers glances a few times. Eventually I went up to her to talk to her but the response I got was really cold. I made small talk but she gave one word answers, so I just sort of left the conversation because I thought that was really rude of her or that she just wasn't interested in talking to me.

After a while we were both dancing near eachother and I noticed that she kept bumping into me. I didn't really know how to react because I thought she wasn't interested, but she kept looking at me. There was a few times where I would turn around and I could see her looking straight at me. She would quickly avert her eyes and run her hands through her hair. This happened about five times altogether so I knew she was interested.

Anyway, I had to leave to meet up with some friends, but I managed to find her on facebook a few days later. I asked her if she wanted to go for a drink sometime (I know it's lame asking a girl out over FB but I didn't have her number. Please don't judge me!) but she didn't reply.

We've both been invited to a party this weekend and I'm bound to run into her again. How do I talk to her without her getting all shy on me again?

Especially looking for advice from girls, especially if you're shy too.