Katherine borrows a sweet moped with pink tassels on the handlebars and flames on the side from her friend Rebecca when she visits the island of Martha's Vineyard for the weekend. Katherine's friend Charlie takes off on the moped and rides out to the beach for the day, forcing Katherine to rent a less cool, flame- and tassel-free moped from a local shop. Who may Katherine be able to hold liable for the cost of the moped rental?