As everyone else has said, there is NOTHING a guy can do to "make" a girl like him. Even if he is exactly what she is looking for, if she has already put him in the "only a friend" mold, she will probably look at you as a brother, and thus, not sexually (I would hope).
You say she knows you like her-this leads me to believe that if she felt the same way, she would have let you know by now. If not, she may just like having a close friend whom she knows is attracted to her.
If your friendship is what is supremely important to you, than just make sure she knows the ball is in court, but you'll remain friends regardless. If, however, you do not feel you could "just be friends" with her, than tell her so, and tell her why. Maybe you are overestimating her knowledge; as conniving as us girls can be, sometimes when we find out someone likes us, we think, "REALLY? Get outta here!" when it is completely obvious to everyone else. Just be honest with her...but the outcome is not guaranteed.
I love to ramble!

Cherry