if you buy any plant from a shop it has probably been treated with pesticides and fertilisers etc, so you need to remove from the pot, wash the roots and repot in chemical free soil and leave for at least a year for any chemicals that have been absorbed to grow out. if you know of anyone that has any suitable chemical free plants and tort safe plants then pinch some cuttings!
As Blackdog says spider plants are good and safe if nibbled and the tortoise table has lots of other ideas.