I think being ready is a completely subjective thing, there is no list of signs that mean you're ready.
The most basic way to know if you're ready is if you feel that you are.
This reminds me of that question many young girls ask themselves, how do I know when I'm ready to lose my virginity? Well, you just know... if you have to ask, then you aren't.
Keep building up the friendship. Even go so far as to tell her you have feelings and you think she does too, but you're not sure that you're ready to pursue it. Once it's out in the open, things may begin to develop naturally.
I try to live my life by the motto "go with the flow." Sometimes I forget and get caught up in trying to control things that can't be controlled, but I always feel much happier and at peace when I just let life happen.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker