The roots of the plant may make it hard for her to dig. She may also eat the soil somit needs to be a type that won't harm her. How are you going to dig the eggs up to count them if she lays them there?
She should get fat in the back end of her body when she's gravid. Her background color can go almost black but may not too. It's often hard tomtell which is why we put the laying bin in the cage and leave it there. When she's close to laying she will roam the cage looking for a laying site, likely drink more, may eat less, etc