Girls..answer this..why is she actin like that..?

Well it sounds like she's acting like that because she's hurt about the way your sister behaved and she doesn't want to get involved in all drama. By getting your family involved (even unintentionally), you made it more complicated that it needed to be. All you can really do now, if you want to be friends with her, is try and talk to her in person and apologize for what's happened, and explain it all. If she still doesn't want to talk to you after that, then at least you would have your answer and you can move on.