If she is adding you to an exclusive group of confidants, then she is clearly very close to you. However, this doesn't mean she necessarily like-likes (fancies) you. Either way, take it as a good sign. It shows how comfortable she is with you and how much she trusts you. Good friendships have great potential to turn into relationships, so if you are interested in her carry on as you are. Whatever you do, don't put pressure on her or ask her how she feels. She should show you how she feels about you when she is ready.
In my case, I had a best friend that I was close to. I broke up with my boyfriend and confided all my problems in my (male) friend. I became much closer to him and some feelings that had been quietly bubbling away flared up. I completly fell for him. But it all started a with a platonic friendship.