I wrote you a very insightful and understanding response and, for some reason, it never posted. Now I am so tired and bleary-eyed, I can barely put a sentence together. So, I will simply say that it is difficult to understand why people who are miserable go out of their way in order to make someone else even more miserable than they are. I am glad that you are remaining mature and refusing to stoop to her level. She will eventually be the cause of her own destruction because people like her always are.
Please don't let this cause you any undue stress and continue to be the better person - because you truly are.
Peace and Blessings