It's really simple. Hand her a bible and ask her to find you the reference in the bible that says snakes have anything to do with the Devil. For that matter you could ask her to establish that there is in fact a devil but lets take some baby steps with her. If she comes back with "Because you have done this ... on your belly you shall go, and you shall eat dust all the days of your life," (Gen 3:14) Kindly inform her that your snakes do not eat dust. They in fact eat rodents. This bible verse sounds like its describing a common worm more than a snake. If she insists that that was a snake then throw this one at her. Mark 16:17-18, in which the risen Jesus tells his disciples, "And these signs shall follow them that believe; in my name shall they cast out devils; they shall speak with new tongues; they shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover." If she believes why hasn't she taken up serpents?