I hope your cat has just gone into hiding with her kittens. We had a feral mum that we fed in the garden (Jessica in the picture below) and she went off to have her kittens. After a couple of days when we didn't see her, she came to us twice a day to be fed. She didn't bring the kittens to us until they were 9 weeks old. I hope this is the case with your beautiful tortie cat.