Hi Blessed,
Having gone through the BCG treatments myself, I think I can understand your Grandmother's concern about protecting her dog.
I would recommend for her to be consciencious about keeping the toilet seat down during the time the toilet is being soaked in bleach on the day of treatment. I would also double check to make sure that the bathroom door is closed as a double safety net. That is what I would do. I would just check, check and double check. I think if she does this the dog will be allright.
I'm not even sure what you would do with a Depends adult diaper if it had absorbed BCG treated Urine. How would you dispose of it?
Good question though,
Your new friend,
Rosemary