Thanks for your swift reply!

She's currently in a two foot vivarium, the kind that is wood on all sides, with sliding glass doors on the front. I use a ceramic heater rather than a mat heater, purely because that's how I got it second hand. She has the standard stuff in there - two hides, a water bowl, some fake plants, a decorative skull. There's no lighting, so no extra heat from anything like that. I use hemp bedding, which I've never had a problem with in terms of smell, and seems to hold water reasonably well to help raise the humidity, but not quite as high as it should be.

Now I've mentioned it, I'm thinking to myself that maybe the fact it's a ceramic heater rather than a mat heater that could be the problem? However, the guy who used it before me had around ten snakes and just needed to upgrade his old tank, so I assume that he had no problems keeping a snake comfortable in there for at least the first couple of years of its life. I also did do research on snakes and ceramic heaters, and didn't see the humidity as some sort of reported problem.