She is most likely teething and will want to bite anything. Feet are within easy reach. Just keep saying no bite and offer a chew for her to bite on. My Uni bites my feet going downstairs when she knows it's time for a walk. I hate this bc I am clumsy and am always afraid one day I will miss my step or she will trip me and I will fall or worse step on her and break or dislocate a leg.
She has always done this and the only way I can get her to not do it is pick her up.