Yes, vitamin D is fine if it doesn't have UV. Glad it wasn't $300. For that much they should have given you a care sheet! Good luck with the gecko.
Aliza
welcome to gecko keeping. I think it's likely that it's a fan footed gecko, though I have never kept that species. Here's a care sheet I found by doing a search: https://reptiledirect.com/fan-footed-gecko-care-sheet/
Your best bet is to do a search (feel free to use duckduckgo.com instead of...
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