facebook question

I have a question that is really bothering me. I tried to add someone a year ago and I think that she refused my request since after that I could only follow her, I didn't have the add friend option available on her account. A few months ago she accepted my chat request and still I couldn't add her as friend, still it was only option to follow. That changed also a few days after she accepted this chat request and now I can add her as friend?! Does anybody knows how did she managed this? Pls help, it is really a mystery for me