Trouble with Friends (girls only)?

My friend and I have a bit of a history she can be a bit "snaky" and this time she weaseled her way in between two of my other friends and I. She started telling them that I was talking about them and all this other ****. I was also a little blind because she has been using me by saying stupid things like oh here them come as they are walking down the hall's I don't really pay attention to this but they heard her, and got mad at me for not "defending" them. And know this has gotten blown out of proportion and I wrote them an email saying sorry but I was so pissed at the other girl, it wasn't a real apology. and now they are even more mad at me, i wrote them another email which is a really apology, but I am afraid to send it since they are so mad at me. I just really need some advice. I can only hear what my mom has to say so many times. this is my last resort. I am breaking of my friendship with the girl who started all this because she always does this to me. and I am done.