Thoughts for Becca:

Do you have a yard? Let the dog stay outside

Does the dog get exercise? A tired dog is less frightening

Can you make a den for Sheldon? A cardboard box on a high piece of furniture, for example.

How many cat boxes do you have? Is the dog getting between Sheldon and his box? That would be a real stressor

Meanwhile, you have my sympathy. I applaud you for helping your niece, but I know I personally wouldn't want 70 pounds of dog in my little home.