I agree with pp. I would also add the many benefits of breastfeeding - including that you are at work MORE because your baby is sick LESS than FF babies
Here is a link that I sent my supervisor and his supervisor to explain why it's best that we continue breastfeeding:
Maybe you could forward to your supervisor? It must be hard for her because she can't have children, but she should NOT take it out on you. If this harrassment continues, I would definitely contact a lawyer These are your personal medical issues - not fodder for office gossip!