Just tell her:I am offended by what you said

and what you said is not true. If she keeps doing so, find a lawyer write a letter to the company complaining about work place harrastment. It does not cost much to ask a lawyer to write a letter and it works. She has no respect to you, so you don't have to give her face. And I think you're a shy girl to fight back by yourself so ask a lawyer is a good way to threaten this.