Maybe you have hard water? Try using filtered water, gallon jugs aren't expensive if you only have a few snakes. Other than that you could "swim'' her in a bathtub every now and again just to get her moving. Or maybe she just didn't want to go yet it's hard to say. Being sedentary ambush predators it's in their best interest not to poop all the time. Mine don't go any more than every four months or so and when I back off their food they take longer, but when they do it's a ton...