Dumerils dont need tons of humidity or heat. I keep my girl with a 86F hot spot with flexwatt and ambient temps of around 77-79F. I will usually spike her cage with misting which she does like once a week or so but the humidity usually sits around 50-60%. She does like to sometimes soak half in her water bowl. Her substrate is aspen only. And she eats like a freakin horse. She was a fat baby.
Your setup seems ok. Baby dumerils are known to be picky eaters which is why you want one that has been eating good. What was the breeder feeding it? How often?
How was the breeders set up? Best to try and replicate everything until you get her eating well, then you can slowly switch out stuff.