I got the impression that her over-the-top responses were most definitely not about you or anything you'd done, even if their language talked about you directly. Like you said in the subject, to me it felt like she was taking out her frustrations about other things on you--maybe because she knew you would "take it." That is, she knew you would be asking, "Oh, is it me? Is it my fault? I'm so sorry, what have I done?" rather than saying, "That was rude and mean, and completely out of proportion to what happened. I don't know what's happening in your life to make you act this way, but I will not communicate with you again until you apologize."
Like others have said, only you can decide if the friendship is worth saving. I choose to have just a few friends myself, and I don't put up with much drama from them. I would also be very angry at someone who sent me a multi-paragraph email attacking me and my life; I wouldn't bother defending myself to them, because I don't have to. I would just be mad, and I would expect a sincere apology with no qualifiers, and better treatment in the future, if they hoped to remain friends.
And also, POD to oceanus.