I'm sorry! But don't let her get to you, nothing is your fault she was just being mean, which now days most people blame others for there problems and lash out at anyone. You just happen to be her punching bag at that moment. Try to laugh it off, I know it will be very hard to do that, but you did nothing and have nothing to be sorry for.
I know how you feel, I've been many peoples punching bag for no reason and it too brought me to tears, but then I had to laugh and just think, It's not my fault they were just being jerks!