Why is my best friend acting weird?

I have had similar situation. What I did was tell her how I feel, how I want the old times back, just the old friend. For me it didn't work out, but I suggest talking to her. Let her know that she is your best friend and you want the good old times back. Tell her that the first time you met her, she was a great friend and that you would like to see her. Try to put this in a nice way, since she might be offended if you say you want the old her back. Explain to her that you like the beginning of your friendship and you would like to relive it.