Welcome to you and your crested gecko. Looking forward to pictures. My two most common pieces of advice:
a 12"x12"x18" enclosure is too small for an adult (I have no idea what you're using, so this may be irrelevant)
just because you don't see your crestie eating it doesn't mean that it's not...
I was just checking to see if she was new and if there's any chance that she has crypto (likely not, but no guarantee. My geckos have had crypto for nearly 9 years and the ones who are still alive are all asymptomatic, but that could change any time). I think diagnosing this is above my pay...
My geckos always fall off the glass when I mist. Will he drink when you're misting the cage? Most of my crested geckos and gargoyle geckos enjoy drinking the drops that end up in the plants or on the glass. If you really feel that your gecko is getting skinnier you could consider a vet visit...
If you can get Pangea where you are try one of the flavors that has insects mixed in. There a fig and insect flavor that may be good. Put some on her lips and hopefully she'll lick it off.
Aliza
It's harder to tell with cresties and gargs because they have the fired up/down aspect that leopard geckos don't have. One advantage of having a lot of geckos is that I don't worry so much about shedding or most other issues until I notice something. I get to check everyone over on feeding...
It's very usual for them not to eat at first and also for juveniles to hide most of the time. Hopefully you'll start seeing poops within a few weeks.
Aliza
Sometimes your gecko can shed overnight and you'll never know. Other times the gecko gets frosty and you can sometimes catch it mid-shed. Just keep an eye on the tail tip and feet and if you see bits of shed hanging there, peel them off.
Aliza
That's a lot of different kinds of calcium. The Repashy pictured there is an all-in-one. Otherwise just pick something that has D3, something that doesn't and keep to your idea of D3 every month or so and Calcium without D3 every other feeding.
Aliza