謝謝您的補充與更正.

基本上您是對的,an authorized card user has no obligation to pay it. 但是在樓主的情況,是他的"朋友"以她的名字申請主卡,所以她是主要持卡人. The card-holder is responsible for the charges of the authorized user, but the authorized user is not responsible for paying any charges, including his own. 加上因為她使用過最後轉帳的master card,所以樓主不能說這是單純的盜用身份的情況,這是問題的重點.