How does Jane Chatham torment the postman?

As the postman is riding his mule and carrying the mail, he sees Jane Chatham on her horse. She pushes the horse to a trot and then a gallop. The horse kicks up plants and grass. She charges at the mule, and the mule is frightened and backs up. The mule kicks up as Jane rides around the postman. His sack of parcels and envelopes falls, and she grabs it. After she sorts through the mail, she returns his pouch to him.