Best thing is to have a chat about the situation. Things can easily be resolved with communication, although in all honesty sometimes people just change. Hope all is well.

You should ask her, what's wrong with her. And why did She stay away from You. Besides, you should look at your self. Is any trouble on you or not?!.

Something must have gone wrong... Find out what was that through a close conversation with her if you can.. Otherwise let her go and wait for another bird to come to your nest. Nobody should ask for a real friendship ;) 

Try to find out why she is distancing herself from you. Make sure you are being considerate though. Maybe she feels like you have been distancing yourself from her and then distances herself further. Sit down and talk with this friend. Say that you feel this way. But make sure you are open to whatever they say. If she truly is a close friend, then you need to resolve this as soon as you can to make sure the rift in your friendship does not become to big to fix.