I don't know what to do about this.

You just need to talk to her. I know it might be really hard to get the courage to tell her how you really feel, but that way youll get it out and feel better. I think your a great best friend for still helping her out even though it hurts. just be prepared because it would be great if she felt the same way about you, but you never know. just tell her how you feel, but make sure you say that even if she doesnt feel the same way you still want to be friends and that youll always be there for her no matter what. then maybe once you get it out and she tells you she doesnt feel the same way youll be able to move on easier. unless she likes you back then thats really good. you just have to talk to her.