dont use soil as some companies use chemicals in their product. be sure the soil is NATURAL and chemical free.
Best is to you use the coconut husk i believe its called that and break it down and keep it moist. Its the bedding in a brick you get wet and what not. Either use that or anything else that snake owners use to keep humidity up.
and to help get her back up to weight feed pinkies once a week to help out a bit.