god how awful - you poor thing. is she a teaching member of staff, i.e. do you spend much time at break / lunch in her company? If she is, then shame on her - she's acting like one of the worst behaved children would. Even if she isn't, the situation is still intolerable. Who told her that her behaviour was unacceptable? Whoever it was, I would go back to this person and just fill them in on the attitude she has displayed towards you even after being told not to. Her behaviour is very unprofessional, whatever her role in school and she needs to be taken to task by her line manager.
All the best - how horrid that you should have to endure this when you're doing something so positive for the school (repeat this to the person you speak to as well!)
Roll on Dec 17th, eh?