Tell her that there is a new technology now deployed that will decypher the text tones and it is all being recorded and archived along wiht the cell number the data is being transferred over. She will think you are kidding but don't give in.
I told a person once who threw cigarette butts out that the DNA libraries were being established based on the cigarette butts and they could trace her every move. She believed me.
(edit -- I can't spell for crap).