It seems like you have been acting like her friend from the very beginning. That's the problem. A lot of guys come across a beautiful woman, and they "play it safe," by being friendly (friend-like), and then are surprised when they fall into the friend zone. If you want them to be your lover, you need to be their lover. It's ok to be a friend AND a lover (in fact, it's kind of required if you hope for an LTR), but lover needs to be in the equation in a big way.
You need to flirt and build Sexual Tension. Flirting is basically the art of witty banter. To give you an example, I was flirting with a girl I'm dating last night. I told her we couldn't go paintballing because her height gives her a huge advantage (she's real short), and she said "are you calling me short?" Then I said "Not short, fun size (laughs)." And then she said something about her sister being shorter. So I said "It's ok, I like fun size!" So it seemed like I was mocking her, but it was funny, and I turned it into a compliment, and she really liked it.
If you are bad at flirting, I recommend watching comedy movies, comedy videos on YouTube (RayWilliamJohnson is the man, just sayin'), and books on writing comedy or doing stand up comedy. But it's not all about being funny, you need to be romantic and sexual as well, so you mix that in.
Eventually, you're going to have to take the risk. You're going to have to start flirting. You might get rejected, but at least you tried. Remember this: women are emotional creatures. Your goal is to inspire certain emotions in her, and arousal.