How do I get closer to a friend? (girls)?

This friend of mine is more straightforward and caring than anyone I know. I've known her for a little over a year through mutual friends. She was in a relationship but it ended towards the end of 2008. I asked her on a date in February and again in March, both times she said she wasn't ready. I have friends over to party all the time and she shows up once in a while, I see her at friends' houses. She knows how I feel, and she is always happy to see me, greets me with a warm hips-touching hug. Then again, she's happy to see everyone, that's just her personality. How do I win her over, and what should I do to make sure I don't blow it?