It made me sad to read this. I don't agree with punishing a child so severely (or at all) for having accidents. You and the parents must be feeling at your wits end and I gather from your post that you don't entirely agree with their methods. Usually there is a reason for this. Some sort of familial change, sexual/physical/emotional abuse or medical. Have they ruled out medical reasons?

If the child is having accidents at home as well then how can your program be blamed for her accidents? How is a "non stimulating environment" causing her to act out in this way and how is taking away some of that stimulation going to help her?

I like the idea of taking the pressure off of her. You might just find that she stops altogether.