cousins

Male giving a ring to his married cousin

Q: If a girl is married and in a joking form if a cousin brother gives her a ring and told her that this is an engagement ring, then that girl denies is and then he said he is just kidding and the girl is sure that she is married and she doesn't take her cusion brother more than a brother, so she took this as a gift and wore it on the right hand and when he left, she removed it. Is her nikaah with her husband effected?