Try alfalfa pettets made for horses...comes in 50 lb bag at tractor supply. Put a 2" layer.. It is very absorbant and you can clean out only what gets wet and throw it directly into your garden ..it is biodegradeable and good for plants. If the tort eats it ....it is actually healthy for her. Stock tanks for livestock make great "boxes" for tortoises...they are waterproof and strong...will not hold odor like wood.