Treat others how you want to be treated..

So my best friend is kind of a selfish person. It never really bothered me. But lately it's been all about her and I can't problems of my own because he's are much worse. So lately I've been treating her how she's been treating me. And she has not liked it one bit. And part of me feels bad, but the other part is like she needs a taste of her own medicine. I'm just so over the way she treats me! I still want to be friend becuase she is a good human, but sometimes she needs to be out in her place.