Mistress Valentina was pissed at the way in which this girl behaved and she had to correct her and make her act in the way she wanted. She had tried to talk to her but the girl sneered at her and did not make any changes despite being told how beneficial it would be for her to make those changes. So the only option available to the mistress was to trample her and teach her a lesson which she did by trampling her and gagging her.