Because behavior is usually impossible to decipher, we must all strive to put our feelings into words. Thus, there is only one angle to take--get her to translate her behavior into words.
The question is how can we help your friend to verbalize what's going on inside her? To start the process, you can call or write and say,'I sense a cool breeze blowing from your direction. Did I say or do something to turn you off to me?'
If she says everything is fine, then you can say,'But, your behavior indicates that everything is not fine.' Then detail the changes in her behavior, such as you avoid me, don't call, etc. and ask her what this behavior is saying to you. Notice that the goal here is to open a dialogue, ask the person to translate his or her actions into words.
Here's another key point, in order to invite the person to talk, you must encourage them to be honest about whether you said or did something upsetting. Opening the door in this way, usually paves the way to a discussion.
Doing what I suggest, should help you clarify what's wrong. Then you can take the necessary steps to repair the problem.
And, by the way, women as a group aren't complicated, per se. In fact, most humans beings are complicated because we have never learned how to put feelings into words.
Relationships are troubled because people act out their feelings through various behaviors. The problem with acting out is that actions are hard to interpret and actions usually damage relationships.
In order to have working relationships, people must talk, not act, and they must talk in constructive ways, simply stating what was said or done, and then COOLY describing how the upsetting words or actions felt. I call this my XY Formula (I felt X, when Y was said or when Y was done.)
Beware that even if you get her to talk this time, you will probably run into this problem again with her because she tends to act out feelings when she is upset. So, you might want to lay the groundwork for a healthier way of dealing with future problems. To do so, you might say, ' Can we agree that in the future, when I say or do something to upset you that you tell me right away?'
Good luck. You should be able to work this out.