If you're really that concerned you'll have to take her to a vet.
There are a lot of variables in a change of appetite. Just the fact it's winter could be contributing to that.
But there's no need to get worried so early on. Keep monitoring for a while longer. And trust me, they sleep in the weirdest positions.
Mine sometimes sleep with her leg hanging out her hide in what looks like a physically impossible movement let alone comfortable.
Just saw your post: It's hard to comment on correct supplementation. After all it's your reptile. But what you're doing is widely the accepted way.
Personally I use Repashy Calcium Plus. It has everything a leopard gecko will ever need and you use it on every single feed. No need to change.
Also what age is she? She might just need to pace her eating a bit.
If you have any concerns, doubts or worries about your animals health always consult a qualified veterinarian (with the necessary experience).
Nobody can properly diagnose an animal based on descriptions and photos. Especially when those animals, such as reptiles, have a small list of visible symptoms than can be found across a large range of problems.
Always see a vet. Don't let strangers on the internet make you do something you'll regret. They won't take responsibility.