Mares often have sensitive skin at this stage and they can become very possessive of their food. If you feel threatened it is definitely ok to correct her firmly, better now than later if she’s going to be protective of her foal. She has a lot of hormones affecting her right now as well, but I highly doubt it has anything to do with the gender of the foal. In response to an above comment I also do not recommend imprinting the foal as research has shown it can create hypersensitivity in the foal. Always consult a knowledgable equine veterinarian with behavior experience if you have any doubts or questions. Good luck!