Believe it or not, one of the surest ways for passion/interest to blossom is just simple proximity. Keep doing what you're doing but sit just a little closer to her than you have been. Begin (non-sexual) touch, punches in the arm, play wrestle with her if she will, etc. Forget what she won't admit. Falling for someone is largely an unconscious process anyway. There's absolutely no mileage in going there. Just keep up the proximity and a little romantic tension, and it may blossom. That's how I've moved out of the friend zone, anyway. You see romances all the time that spring from friendships. This is how it happens.
You do have to "calibrate": to her. You have to study her body language and facial expressions to see if you're crowding her. If you move closer and she turns away or closes herself off then you're too close. If she's turned toward you and engaged, move just a little closer. Slow and steady wins the race. (If what I'm saying here is greek to you, you need to get a book on body language.)