keep your cool as much as possible

chinese people are not good at controlling tempers. being hysterical does not help. it'll only make you look unreasonable and any justification you had may be lost in yelling or resorting to foul languages.
in your situation, i'd just say "what? i am being nice. this is how i talk and i mean no offence to anybody. anyway, you should mind your own business and then maybe you will not take other people's card as yours." if she keeps bothering you, you should ask the clerk for security about harassment.