We have a homebred 7 month old TB filly, who has been perfectly sweet and trouble free until now. She was weaned a month ago and although she was getting a bit big for her boots just before weaning, having the confidence of her mother to fall back on, she quickly fell back into her easy to handle attitude after weaning.. However, quite suddenly, she has started behaving agressively - ears back and trying to bite. Nothing has changed in her daily routine and she has another filly foal for company. I am curious about this sudden change. Is she challenging me and if so, how should I react ? At the moment I just wait patiently for her to get over it, but not sure if I should be being assertive.