Strange Famous, if you read through this board you'll find all sorts of threads along the lines of, "This girl is giving me mixed signals..." and guys wondering what is happening. It sounds like you're in a much better situation, so make the most of it. Forget the yawn-stretch-arm-around-her routine. Next time she leans into you, just put your arm around her as if it's the most natural thing in the world. Also, to give you some completely original advice - just kiss her!
And above all, have fun!