Why do you feel that if she likes you, she has to
enter a relationship with you?
Understanding this point and from www's wise words - life
is not about BGR. Her answer doesn't drive you crazy - it
is your expectation of an absolute answer leading to some kind of
direct conclusion that is killing you.
Here's truth number one: A woman good in all aspects to you and
herself, doesn't mean she is 'The One'. 'The One' can only be
uncovered with the assistance of time (and sometimes regrets)
because only by then, you will know.
You are expecting a complete yes or no answer - in love, nothing is
absolute. Your signature speaks 'white is white, black is black...'
if love was that simple, everybody would be so happy in their
relationship (or joy without them). 
She is confused over your sudden declaration. Her answer 'Don't
know' signified her inability to confirm with herself to enter into
a relationship with you. You can do two things:
I) Allow her to source for her own feelings. You would probably
give her some private time for her own and if she has feelings for
you and decide to give this relationship a try, she would let you
know a while later in the future.
II) Woo her until you get her. This is straightforward. Because she
is uncertain, chasing demonstrate a side of you, in which by right
should add points and pull up your total score as she is
considering. With time and good effort - either you succeed in your
attempt or make a major flaw during process and turn her off
completely.
Cheers
